Hey dben428, 

If you have access to a physical ethernet connector - then yeah, get a switch/hub/etc.  That's the way to go - that this notion that your break something from your ISP, well thats a bunch of hogwash (I've always wanted to use that word). 

The issue with WiFi-USB route really has to do with the OS.  Unless you're running a script to keep the connection alive, it'll most likely die - and (at least with cgminer) a dead network connection means a reset to your mining pool and a lot of down time. 

One thing to consider too, case - or at least how you're going to keep the system to physically stand.  I'm probably going the Sportswood route. 

Something totally different - after thinking a bit more (and after some coffee in the afternoon), who else is just going to grab power for their Pi directly off the ATX PSU?  I figure that I'll just piggyback off of here for my Pi's needs - you'll need to have one anyways.  I was thinking about some of the more complex (yet cooler) solutions - but simple is best.