$4 is a decent price for short USB extenders but dx.com has 'em for $1.50:  http://dx.com/p/usb-2-0-extension-cable-20cm-28982

@dwdoc: All of the Amazon feedback on that hub is bad - have you noticed any high-pitched whine? And is it still behaving well?  The clearly confused product description (I'm guessing "2.5V AC adapter" means "2.5A AC adapter") doesn't inspire confidence either but if you still like yours I'll probably order one too.

@Nemo1024: Thanks!

@lano1106: I'm running Ubuntu on the PCs and I installed minepeon on the Pi last night since I have a 7-port D-Link powered hub coming today. 

@myter_miles: I'm sure a PCI card would work but I'd prefer the flexibility of a hub, plus you aren't taking up a PCI slot.  I wouldn't bet on an internal bay since they're usually powered by a single cable off the mobo.

I installed Minepeon on my PI last night and confirmed that my small powered hub will run more than 1 Erupter so when the D-Link shows up tonight I'll post if I have anything new to add.  If you haven't seen MinePeon I highly recommend it.  The devs did a really nice job in automating everything I've been doing by hand for a while.  And yes, I'm donating some of my mining to them - they've more than earned it.