Building file server / minecraft server / xbmc based htpc for living room. All running on xfce debian stable. I have everything figured except the graphics. I was going to with a simple dual core pentium until the htpc idea came to me. I don't know if that will be enough to drive dvd player. I can upgrade to an i3...
I've currently got an HTPC with an AMD A10-5700, ASRock FM2A85X-ITX, 8GB of Samsung magic RAM, Silverstone ST30SF, Samsung 830 120GB SSD. It's a pretty peppy system already, and will play a lot of games without issue. This HTPC pulls mostly XBMC duty, although it sometimes also pulls Steam light gaming duty.
I've been running an HTPC since 2009, and love the thing. I am currently running MediaPortal, but think I am going to switch to XBMC for the frontend (currently setting it up on the laptop to make sure I like it before putting it on HTPC).
Before I built the HTPC I had visions of it being much like how an AppleTV or Roku is today, basically load the frontend and stay in it 95% of the time.