I think the need for USB 3 sadly is going to come in terms of a move towards USB in general
I love Firewire, i have a MOTU 828 mkIi and its great, however as of my last laptop purchase its kind of becomming obsolete.
Laptops are no longer coming with Firewire, or sadly even PCMCIA anymore or certainly not at the lower price points, and I don't particularly want to pay out twice as much for my laptop becuase i like having one to mobile record its not my main DAW.
Previously i had the option of recording mobiliy to my laptop through the 828 then moving to the main DAW and still using the 828. Now I am going to have to look at alternative soundcard for mobile recording.
The good news is the best USB soundcard on the market for my purposes is funnily enough the V-Studio 700 by cakewalk. The only other thing that comes close is the RME USB alternative.
The fact that both RME and MOTU long term Firewire champions are moving towards USB speaks volumes.
The simple fact is that most Desktop and Laptops of the future are going to have one connector type USB 3.0 even the new Light Peak protocal is still going to use that Connector type for compatability.
I am now holding off because i am waiting for USB 3.0 to maature and to see who produces the first USB 3.0 Audio Interface with 8 mic preamps and at least 8 in/out via ADAT, ideally 16.
The other thing that this could give us would be extra DSP
Personally my ideal soundcard would be the following spec.
USB 3.0
8 Mic Preamps
16 (or more given the bandwidth of the new protocol) ADAT in and outs
DSP reverb/comp etc that can be used both for monitoring inputs so i can give vocalists a good sound while still recroding dry. But also that could be applied during mix to take some strain of the PC (i think that this would be a better use of the other Half of the v700 that the Roland Phantom they have bolted on.
This should all be possible via the new protocols bandwidth with the advantage that again in 2 years once USB 3.0 is ubiquitous that it will work with whatever computer i buy, and probably for the next 5-10 years.
If M-Audio bring out a soundcard with similar spec to which i have just described i would probably buy that becuase sadly having Pro-tools of some flavour is still going to prove useful in terms of collaboration.
Edit
INterestingly enough the new MACKie firwire mixer is now compatable with pro-tools m-powered, and this is available as a $50 upgrade driver from there website. THis suggests to me they are paying some form of license to Pro-Tools to provide compatability, I think that Cakewalk shoudl look into that. Not making it a standard part of driverware, but having it available as a download like the MP3 encoder is.
In that situation i would buy the V700 no questions asked, its the best thing out there at the moment, and it would still let me collaborate with the die hard Pro-toolers.
G