I'll be honest that I haven't heard much good about it. But then again I haven't heard much of anything about it.
From other comments I have seen, I think that it might be hardware-picky and not play very nicely if you decide to swap some hardware later on (don't quote me on that though...do some research on it yourself to be sure).
Honestly, you could build a custom media center for much less than a media center pc and have it work just as well. My computer has been running as a digital video recorder for over a year now with great success (I use it just as a normal computer, with it recording television in the background most of the day). That is thanks to BeyondTV (
www.snapstream.com). Best software purchase I ever made. But there is also their main rival, SageTV if you want to look into that.
I'm starting to sound like a snapstream commercial now probably, but they are also hard at work on a product called Beyond Media that is intended to be a Media Center-like interface for all of your digital media (music, dvds, tv, photos, etc). It is currently in beta.
My opinion? If you don't like to tinker with hardware, then get a Media Center PC. For the most part it should be plug-n-play and easy to set up. But if you like to be more hands on, put together a cheap pc (don't bother going over 2ghz processor, but put in at least 512 MB memory and a really big harddrive or two), throw it in a mini case like a Shuttle. Get a low-end graphics card that has TV-Out. A DVD-ROM if you want it to play dvds. A decent sound card that can output to whatever type of speaker setup you have. And (if you want it to record TV) the coup de grace: a Hauppauge PVR-250. The pvr-250 is a hardware MPEG2 encoder. You can record incredible quality video at only a 1-10% utilization on your processor.