I use my htpc for dvds, divx, music, net and emulators. Definintely dont use it for pvr though. It wont record as well as a dedicated pvr box, which usually have two tuners so you can record one and watch one, or record two and watch a recorded. If you have digital cable youll also need to jerry rig a ir blaster to have it change the channels for you, not to mention figure out a way to get proper listings (not always as easy as it sounds).
PVR is more of a headache than its worth on a htpc as far as im concerned. Time warner gives me the tivo box for 8 bucks a month.