I use a Media Center (complete with American spelling). currently 5 freeview tuners, 500G HDD, and the ability to watch anywhere in the house via extenders...
To Gaffers. XP MCE works OK given 1G RAM, but really needs weekly reboots. VMC (Vista Media Center) is more stable, but places higher demands on hardware. Mine has 2G and a 3.2G P4, video supplied by Nvidia 8500GT card. Admittedly, its got 5 tuners, so can be busy sometimes, but sometimes I just get the feeling it could do with a bit more horsepower.
The thing that really kills reliability is installing those dodgy 'codec packs'. Absolutely not required. MPEG2 decoder (for XP MCE, VMC has one) and a single codec such as ffdshow is all you need, and massively increases reliability in my experience.
Anyone using media center, and have a static IP (or dyndns etc configured), check out an excellent add-on (now free I believe) called WebGuide4 by ASCII - use a web browser from anywhere on internet to record that program you forgot, or even watch stuff you've recorded. As music. And photos. Bloody brilliant! I frequently record programs from my phone...