I've had a mission critical Media Centre PC set up in the living room for the last - oh - dunno. Since MCE 2005 came out.
It's had various interim builds of Windows Vista running on it for various lengths that were abandoned for various reasons (and she beats me if it fails).
As of RC2, my setup was stable enough to keep, so the leap has been made.
It's not a completely flawless upgrade (things improved 400% after a BIOS upgrade, I might add), but it's solid enough that I can leave it running and not be super-scared that my recordings won't happen. The PCI tuners work well. My 6600-straight 256MB card is a little slow when mixing UI with video, but it's gradually been getting better, so will probably continue to improve with new drivers.
The new layout took a little while to adapt to, but near-accidentally addresses one of my criticisms of earlier versions - anything sorted by Date should sort Descending.
It doesn't actually sort that way, but that's OK - instead of having to scroll all the way to the bottom of a date-sorted list, you can just hit Left once in a screen-wide-and-wrapping horizontal list, and you're at the most recent block of entries. That's a time-and-battery saver right there!
Anyway, we're very happy together (thanks for asking). RTM should be good.