https://bitcointalk.org/index.php?topic=253749.0Do not make the same mistake as I did! DONT USE USB 3.0 HUBS for Raspberry Pi... It doesn't accept USB 3.0 hubs at all. You can run BFGminer or Minepeon to make things easier...
The RPI is a great little standalone CPU that can take up to 49 USB miners (thats what I read at least). I use 4 of the the DLink 7-Port hubs connected to a Rosewill 10-Port hub running 20 Antminer U1's. I think the RPI is pretty neat since its customizable, and can be a standalone unit. I have mine in my room with a wifi dongle.
I don't think the U2's would be too different, but do take into consideration that the U2's have a thicker heat sink, so get a hub which can accommodate a handful of these to save you money on hubs.