Huh, that's curious. That does make sense, though. The Wifi adapter itself has to suck at least 500mA out of the plug, and bringing up USB must do it.
I did a few other things, I tried adding a debugchumby file to a Flash drive and plugging it in, thinking maybe the clock overlay trick I did last night was making it bootloop (haven't restarted it since then, so I haven't even seen the clock yet). But it never even brought up the flash drive. I also tried "special options" mode which reboots at about exactly the same time in the startup process.
Curiously, I plugged the Chumby into another, identical, power adapter here at work, and I would constantly get only a white screen just before the colored googly eyes, just as the screen usually flashes. Power button wouldn't even work. Maybe these things aren't really capable of 2A draw
Well, one thing's for sure, though: with all these hard crashes, I'm glad it's Flash based