A couple recent notable comparison tests between a Microsoft Media Center Edition PC and a standalone TiVo have been making the rounds: TiVo versus Media Center Edition PC's - finally! and Media Center Eye for the TiVo Guy.
In both sets of tests, the Media Center Edition PCs prove to be a bit buggy and crash-prone, and the reviewers eventually give the final nods to TiVo with its bulletproof simple design and reliability.
Michael Gartner, a media analyst and a big fan of MCE, counters with the mention of all the cool things you can do with a recorded show on a PC: archive it to DVD, stream it with other computers on your network, and copy it to a portable device.
What it all comes down to is how you want to view and consume media. For most folks, they just want a dependable box that will do what they say. In a way, it's a lot like a helpful robot. You say "tape all the Sopranos you find" and you expect it to do your bidding. If you want to do more, you'll have to hack around a bit or throw some parts and free software to build your own, but a minority of folks seem to go to such lengths. That's what came out of a recent discussion of building your own PVR on MetaFilter, where even hardcore geeks admitted that it was much cheaper to just buy a tivo, set it, and forget it, when compared to the parts list and nuturing that a linux-based PVR requires.
I think that's the bottom line to all of this talk. If owners want to burn stuff to DVD or watch shows on their laptop while traveling, it's probably worth using MCE or MythTV, even though it costs more and they might crash from time to time. But for the vast majority, an $80 TiVo box will serve their needs, can be trusted, and hopefully if TiVo can get their "TiVo ToGo" features released soon, you'll be able to do many of the things that MCE boasts as advantages.