The XBox 360 is my Media Center PC. I got the $10/Month Netflix subscription along with the ~$3.50/Month Live Gold membership. I am able to stream all the on demand Netflix content (in addition to 1 DVD out at a time via snail mail), most of it in impressive HD to my TV. The 360 also connects to all of the other PCs in my house and can stream music, pictures + video (including divx/h.264/mpeg4 movies) to my TV from those PCs.
With the XBox you get a fairly quiet PC, HDMI, a very stable OS... all for a price of a barebones HTPC (case, power supply, motherboard... you'd still have to add the processor, hard drive, memory...).
You won't have blueray or DVR functions. I've considered rolling my own DVR but the dish network DVR I have is just too good. I wouldn't even come close to functionality/ease of use.
If you really want blueray... buy a PS3 too!
You could probably get a 360, PS3, 1TB NAS setup and 1year Netflix + Live Gold Membership for about the cost of a good HTPC rig.
If you insist on rolling your own, check this out...
http://linuxmce.com/http://video.google.com/videoplay?docid ... 9829&hl=en