As a little update on the status of the coding: I had to make an unexpected trip home from college this weekend, so I'm going to be a weekend behind on this project. The aim now is to get a mostly perfect version 1.0 sometime next weekend.
linux box, I haven't seen the program surpass 12 MB of ram and 5% CPU. The 5% cpu only happened when it was searching for devices or getting absolutely spammed with HTTP requests (50 requests/second). The normal CPU usage when it isn't doing anything except waiting for an HTTP request is 0%. I'm sure that once I add a rules engine, there will be a bit more constant CPU usage, but it should really just result in similar, quick spikes of only a few percent. Overall, I've designed this for efficiency in terms of both CPU use and ram accumulation since it is designed to run long term without being touched on low-power platforms. Eventually I would like to get it to run on something as low power as DD-WRT router.
http://www.pandaboard.org/ that will replace my current x86 pc, sheeva plug, and wireless router in one fell swoop. The existence of openMobile makes that look more possible than before.
Anyway, to be make your decision a little more cloudy, here's some pros and cons I can think of right now:
-The wifi sheeva plug also adds more features. Whether you need them or not is up to you.
-USB wifi cards may consume more or less power depending on the card
-Many USB cards offer poor performance (although this doesn't require much)
-I'm not sure if the wifi sheevaplug has an onboard IPEX connector for an antenna, as an antenna will likely make a big difference.