We already have people running saffire pro 40s  on thunderbolt flawlessly. In some instances they perceived performance to be better than before (which of course cannot be true, it simply is the same). That's pretty impressive. Focusrite says there are no issues with thunderbolt either. So until you can find me just one example of how thunderbolt can make FireWire less efficient, or actual issues where thunderbolt has incompatibility using firewire devices with adapter, I will simply assume your assumptions are based on mumbo jumbo rather than reality. And thunderbolt will be backwards compatible with later revisions so the adapters will always work. To say firms will stop selling adapters utter baloney, thunderbolt would have to die first, unlikely with Apples backing.

Well, to close the firewire/usb/thunderbolt thing, I would just say that:
 
Nowadays:
*ALL computers support USB, either 2 or 3.
*No laptop support firewire anymore. For desktops,you can still find addon cards and mainboards,but they tend to be a bit old.
*Few laptops and desktops support thunderbolt. Just check the number of mainboard that have thunderbolt compared to the ones that don't have it and we'll talk about it again. Moreover these cards tends to be on the expensive side. Too, there's still no PCIe thunderbolt card to add thunderbolt to desktops which do not have it (one has been announced by intel, but we don't know when it'll be out and how much it will cost).
 
So:
Yes,firewire is a bit better that USB2, but it's just a "on the verge of death" technology as were SCSI(which was better that IDE), Floppies, HD-DVD, etc..
 
I would definitely not take the Apple Firewire adapter to be something granted. Apple just care about Apple and it's definitely not sure they'll maintain drivers for windows for a long time.
 
The important questions are:
Will the soundcard enable me to do what I want? 
Will I be able to use it on my computers to come or do I plan to change both?
 
Personnally, I don't know if my next computer will have thunderbolt or firewire. Thunderbolt is expensive and not mandatory on current PCs. Firewire is dead. I just know my current core i7 laptop only has USB 3.0 and that my next one will have USB 3.0 too. My desktop has firewire and USB 3.0. I like to be able to use my DAW on both so choice is quite simple.
2 monthes ago, I bought for my band,a new soundcard/PC . I had to downgrade CPU to get a thunderbolt (a shame). When choosing the soundcard, the choice was between an UAD Appolo and a RME UFX. We ended buying the RME which is USB and Firewire. The appolo which is firewire and Thunderbolt ready (500euros more for TB card) was just unusable on the bands private laptops (no firewire and no thunderbolt). With the RME, we are sure we'll be able to use it on any computer available. A very good point since it's good to have some spare in case of a computer crash. Also, the RME handle twice as much inputs as the Appolo, with less latency, even using USB.
 

We're a niche industry. We'll spend a lot of money for slight improvements. If ThunderBolt can make life better for 1/2 of the home recording market, then I think it'll do well.
 
Main reasons to upgrade...

• handle more mics
• handle higher sample rates

 
More Mics
I don't know if 1/2 of us need the extra through-put. I don't right now. For me, I can already record 16 mics at a time and to upgrade to 24 would be 300 dollars (24 bit 44.1). I wouldn't have to change my interface. I haven't bought the additional 8 because frankly recording that many mics and mixing that many mics is a PIA.
 
So my bandwidth consumption is currently limited by my willingness to set up mic stands more than anything else. Raising my possible track count already isn't worth $300, much less a new interface.
 
Higher Sample Rates
I'm not interested in recording at higher sample rates because of the speed of my computer bouncing the tracks. The fidelity I'm getting at 24 bit 48 is pretty great. My potential track count goes down if I'm recording at 192 because the fiber doesn't carry as many tracks at that rate.
 
Today I can record 8 tracks at 192 and 10 if I spend another 300 or so.
 
I don't mix at 192 because it takes a long time to bounce the tracks and I can't hear much improvement. I have occasionally recorded at 192 when doing 2-4 track recordings and I think I can hear a minor improvement, but maybe they are just good takes. Hard to say.
 
Summary
So for me to want ThunderBolt, I'll need a much faster computer. I think that would be the starting place for me. When my computer is twice as fast as the DAW Jim sold me this year, then maybe.

Funny how exactly the same arguments are being put across for firewire as for thunderbolt. People are using firewire and thunderbolt as interfaces.... now. No USB 3 soundcards at the moment as far as I am aware? So do I conclude USB 3 is dead... of course not!!!
 
" but it's just a "on the verge of death" technology" 
 
No less so that USB 2 - totally irrelevant anyway.
 
To say something will die when Apple is fully backing it (and for firewire adapters also) is a bit of joke frankly, as well as the fact this is actually an Intel product and is featured in HP products amongst others. So you don't trust Apple - join the rest of the gang, that's not a particularly good argument however considering this is one of the most successful IT companies in the world (like it or not they can buy small counties with the money they have).
  
There is no doubt that USB 3 is probably going to be far more popular than thunderbolt, just like USB 2 is far more popular than firewire. There is every possibility of this becoming a niche product or at least a good replacement for people who already own firewire devices, just like there is every possibility of USB 3 soundcards coming out next year, heck I may even buy one.
 
These are facts, everything else is just your own biased opinion based on no facts other than you prefer maybe green to the colour blue. And you think something is a bit old.
And NOBODY will know what will actually happen for another year, you are not Nostradamus nor am I. And probably the opposite will happen to what you or I will think, you just have to look at history... Amazes me that people think this is a game of top trumps, it is not.
 

 In answer to his original question, I don't think there is any reason he shouldn't use a USB interface. The average home studio recordist who tracks a small number of tracks simlultaneous probably doesn't really even need an i7 chip unless he is heavy into soft synths, high Track counts. A medium range computer  running 7200 rpm drives or SSD with a basic USB 2.0-3.0 and the Focusrite should do what he needs in stride.
 
 The most prevalent ports on a computer across the board are USB 2.0- 3.0
 
 I'm using firewire right now. Everything purrs along just fine on my Presonus Firetube studio at 24/48 and works fine on Win7 64 bit. I bought a TI card for my desktop MOBO...no sweat. Never rebooted anything,had driver issues or digital noise. Back when I tried USB it was 1.0. I won't even go there...no contest, as others have said USB has drastically improved.
 
 I think USB is simply the path of least resistance for many users, especially if they use laptops. 
 
 When I upgrade my computer it will  have USB 3.0, even so, if my interface is still functional I'll certainly be looking for a way to use firewire again. No reason to change. It works very well.I don't care if it's 10 years old. If it eventually dies or becomes incompatible, hopefully by that time 3.0 will be further along. Focusrite products work well and they don't break the bank to buy, neither do do several others. 
 
 

OP should also take into account the inherent risk of ground loop and other PC usb noises that manifest over the usb circuits (even with USB 2) - a thing that is rare to non-existent in FW (and I assume TB)

joden
OP should also take into account the inherent risk of ground loop and other PC usb noises that manifest over the usb circuits (even with USB 2) - a thing that is rare to non-existent in FW (and I assume TB)

This is one of the reasons I didn't go with a USB interface and stayed with Firewire. Not to mention that the level of performance I've had with FW has been excellent. I'm just hoping that TB will take off in a big way for Windows. 

CakeAlex, we don't really seem to be arguing the same thing, and I've lost the will to continue. Good luck to the OP with his new interface, I say! May he have many happy recording hours :)

1 down 2 more to go ;).

My thoughts is USB interfaces are really only convenient. In my experience any professional audio internal CARD is much more pro...cleaner sound...more stable...etc etc.  But there are times when one cannot upgrade to a card. Such as a laptop.  At the end of the day it doesn't matter what you use as long as it has the features you need to DO what you need to do.  
 
I would stay away from any usb interface (or firewire) that doesnt offer ZERO LATENCY hardware monitoring.