The best companies do write proper drivers for usb devices. The RME Babyface and UFX are other examples. USB for quality tends to be on the minimal I/O simply because of it's lack of bi-directional traffic. Apogee is one of the best companies and reportedly have a Thunderbolt interface nearly ready for sale. Others will follow no doubt. Basically as I understand Thunderbolt, adapters will be available for usb and firewire devices in addition to "native" usage of the TB protocol. Time will tell.

I'm sitting on the fence right now in terms of purchasing an interface. I was/am considering the babyface or the Duet 2 but heard that the new iMacs with Thunderbolt are coming at the end of this month/beginning of May. I basically don't want to buy a new machine now and an inteface only to be out dated already. :)
I'll have to look at the adapters for USB to see if it makes sense to pick up the babyface to use with the iMac until the Thunderbolt interfaces come out. Or perhaps I'll keep sitting on the fence. :)

One of our members already has a Mac with Thunderbolt installed. He says there is only an external hard drive available currently. I'm pretty sure this one is going to stick though of course everyone was positive USB3, SATA6, and 1394-1600 was going to stick too. You could always wait for a new machine until TB interfaces hit the market. I think either the Babyface or Duet2 will be useful in any case for small i/o projects or "note" taking.

Interesting. I heard that Thunderbolt will be on the new iMacs coming. I just assumed that the HD's were internal but was planning to get an external HD for audio. I guess I'll just have to wait and see what comes.

True. At this point, I only need an interface with 2 inputs. So, I could pick up a babyface and then, when I need more inputs, see what's out there in the Thunderbolt arena.

p.s. Here's a link about the rumor: http://www.macrumors.com/2011/03/22/potential-imac-update-to-sandy-bridge-and-thunderbolt-in-4-6-weeks/