First off, I'm not sure that the TiVo OS could deliver data to the USB ports fast enough to make Gigabit worthwhile. But beyond that, is USB 2.0 fast enough for Gigabit versus 100 Base T?

The adapters I mention all spec USB 2.0 as thier basis for transmission speed. I doubt that they will, in fact, make a true 1000 Kb/S, but 480 Mb/s (USB 2.0 transfer rate spec, though running that fast IRL is unlikely, a 2.5-3x increase in speed should be reasonably attainable, though) would do nicely, I think, allowing significantly faster data transfer w/o saturating the local network switch capacity.

Internet access would still be limited to the speed that the modem (i.e. Cable @ 10Mb/s or DSL @ 1.5Mb/s, for instance) is capable of, but the local network speeds for data sharing/transmission would increase appreciably. When moving multi-gigabyte files around, this would be a very good thing, IMHO. Bandwidth is your friend!

Since the hardware is USB 2.0 compliant and the Linux OS should be limited only by the speed of the processor and memory access, I would think that unless the processing power of the Tivo is seriously deficient (which series 2 may be, seeing how slow it can be to respond to remote control inputs sometimes), I'm thinking it would be a worth while attempt.

Unfortunately, my experience with Tivo is limited, as is my Linux experience (I can spell it! I'm Winblows trained, so sue me). I do know from some ReplayTV experience that the 10Mb/s ethernet adapter integrated in those units were replaced in many cases with USB 100Mb/s adapters for significantly faster sharing and downloading capabilities. I had it done on my 4505 and it made a world of difference. Unfortunately it's so outdated that control codes for cable boxes have fallen off the map and it won't change channels any more by itself. It's really a shame SonicBlue died and took ReplayTV with it. Tivo is superior, but ReplayTV had some nice features that Tivo lacked. I worry that the same grisly death may await Tivo.

As I said before, the only stumbling block I foresee would be whether there is any native Linux driver support (I doubt it, but don't know enough about Linux to say either way, hence my question) for any of the USB adapters available or how the proper drivers can be installed for the OS to use to talk to the adapter through the USB port.

If there are any Linux mavens out there to help educate my poor neglected brain in this matter, please pipe up and tell me if I'm whistling in the dark. There's got to be a way, I just don't know it.

I would think that the big limiting factor, as you said, would be the speed of the unit. Considering that these units essentially use chipsets dedicated to digitizing, compressing, and decompressing video, I doubt that they'll be optimized for network throughput.

But your points are good - there should be at least a theoretical speed increase with gigabit via a USB 2.0 adapter.