Well, I got around to trying the open source driver today, and it doesn't fare any better than the stock driver (with the latest firmware w/ skype). It runs just short of 10 minutes, and then stops picking up packets. According to kismet, it's still hopping channels, but just not picking up anything. I've told the device not to scan for access points, and set the wifi timeout to never through the control panel, so I would think that would take care of power management issues. The backlight going on or off, incidentally, doesn't affect how long it scans for. There's something at a low level shutting down the chipset, whether it's plugged in or on battery, at about 10 minutes.

Incidentally, I happened to be listening to some music while I waited for it to timeout, and it caused the music to pause for about 1-2 seconds, with a CPU spike, while it did whatever it does to power down the chipset. I'll try running top with a fast update the next time I try, just to see if I can catch the process that's doing the dirty work.