I'm using ThinkPad laptops as my BTV link boxes (see .sig for details), and believe it or not, they work fine for HD playback. They're also extremely quiet and generally unobtrusive. Of course, the downside to laptops is the relative difficulty (or in some cases, the lack) of upgradeability. I'm using them now because they're available and they work. When I finally get around to upgrading them, I'll be able to build the next-gen Link boxes to spec: PCI-e x16 slot, laptop HDDs, passively cooled video card, HD-DVD drive, whatever.
So count me among the number of folks who prefer the control, customizability, and upgradeability of a dedicated BTV Link PC.
