Just built one, and I really enjoy it, have a Core Duo CPU, 500gig HD, Blu Ray DVD, dual HVR 1800 tuners, RF wireless keyboard with a trackball and finally got ahold of an 8800GT card.
Am locked into DTV for another 9 months or so, but will swap over to cable once that contract expires and use the HTPC to replace my DTV/Tivo unit with no Tivo fees.