Home Theater PC

So who all has one as part of their home theater setup? What type of computer is it, what software do you use to manage everything,what's the general setup, and how much did it cost? I'm interested in HTPC's, and all the potential they have to be an ultimate media device(games, music, tv, movies) but aside from some lifehacker articles, I really don't know where to start. Also are there any good solutions for syncing across multiple platforms? So if I wanted to watch part of a movie on my TV, then later finish watching it on my phone I could just start off where I left off. Or if I were playing some sort of ROM on the HTPC, and wanted to sync save states to my phone for play on the go.