Ok, after getting some very useful feedback from previous posts, and reading comments posted by folks like Jim Roseberry - I've identified my next interface (MOTU 896 / http://www.motu.com/products/motuaudio/896mk3). 
 
Currently, the 896 is available as the mkIII (with both USB 2.0 & Firewire). Logic dictates that the 896x will be announced at some point in the next year (like the 828x, it is assumed to be a hybrid USB 2.0 and Thunderbolt device).
 
Should I wait for 896x, or just buy mkIII? Is there even any reason to believe that Thunderbolt is going to blow my mind and change the way I work forever?
 

Thunderbolt is a gimmick in the audio world.  Unless you need a MADI interface with over 500 channels of audio, and even then USB3 would be enough.  For what the 896 offers in terms of I/O, USB2 is fine.  And there will not be any hardware updates to the X model from the MKIII, that would make waiting worth it.  

Thanks. That's kind of what I expected to hear. I really just want to be comfortable recording 24 simultaneous inputs. From what I've been reading here lately, it seems USB 2.0 should be up to the task.

Don't be overly seduced by the "bandwidth" of Thunderbolt.
With 24 channels of I/O, you're nowhere near saturating the USB2 (let alone USB3) bus.
 
Thunderbolt provides external access to the PCIe bus.
Nothing more... nothing less
If you're using a laptop or other small form-factor machine... it's great... as you'd otherwise not have access to the PCIe bus.  For a typical tower/rack, Thunderbolt brings nothing new to the table.  
Since Thunderbolt has yet to "catch on" with the general public, Thunderbolt peripherals are significantly more expensive.

No disrespect meant to Jim or Daniel, but direct access to the PCIe bus is a big deal.
 
Both are correct that the bandwidth difference is meaningless, but bandwidth is not everything, and in fact some would say that latency is even more important. And a well designed PCIe driver will be capable of lower latency than a well designed USB driver. This is changing, and there, reportedly, USB2 and USB3 drivers that rival PCIe drivers. But if you need a rule of thumb PCI, PCIe, and even Firewire are going to have an edge over USBx.
 
That said, Microsoft does not provide official support for Thunderbolt. That's a big problem for most manufacturers, since they risk a lot developing their own driver. If MS does come out with an official TB driver there could be problems, and even if they only make minor changes to PCI it could break an unofficial driver.
 
Food for thought anyway...

Thanks guys. It looks like I'll likely go with the 896mkIII hybrid then. I noticed the 828 hybrid price dropped when the 828x came out, so I'll probably wait 'til summer NAMM and hope they announce the 896x (and hopefully pick up a deal on the mk3, lol).