I doubt you'll get much response to these types of questions on this forum. I'd suggest you go to A/V related sites. Specifically:
thegreenbutton.com (MCE and VMC specific site)
and
avsforum.com (hardcore A/V nuts there.... look under the HTPC forum specifically)
I have Vista, but I don't use Media Center under Vista. I do use Media Center under Windows Media Center 2005 though. From my general observations after successfully using MCE 2k5 for over 3 yrs as a DVR, I'd recommend NOT installing 3rd party apps, plug-ins, codec packs (besides Xvid & mkv), games, etc on your media center if you want it to run stable. Yeah, it kinda defeats the point of have a multi-use computer as a DVR, but if you want that thing to run stable, I've found you can't treat it like a computer. You have to treat it like an appliance. Therefore, I don't surf the web on my MCE PC. I don't install apps or run anti-virus on it. I don't check mail on it. I don't play games on it. Hell, I don't even run Windows Updates on it... Once you get it running stable, lock it down and don't mess with it any more if you want it run 98.5% trouble free. My MCE 2k5 pc runs 24x7, 365 recording HDTV. Has a lockup or random crash maybe 3-4 times per year? Just my 2 cents.