Shuttles can be used for anything that a full size ATX comp. can, the small motherboard has no effects on that.
I've used mine in my sig for everything under the sun, from the latest games like F.E.A.R. and Oblivion (full-res, high textures) to Photoshop CS2 (very fast rendering might I add).
Shuttles are just as fast as any other PC and they dont get very hot either. The lower rated power supplies are not an issue either, as some have tried to claim. For some reason Shuttle XPC PSUs are very efficient. In my old Socket A SN21G4, at one point I had 2 HDs, optical, and a (somewhat)-power hungry 6600GT, never caused a single problem.