If you are a current Windows Media Center 2005 user then you should make sure that your computer has Update Rollup 2 installed. Microsoft has added some features that make this even more useful and usable.
The most useful feature that they have added, in my opinion, is the Away Mode. Away Mode allows the Media Center PC to go into ‘Standby’ but will still record your TV shows and allow content to be streamed from the PC. This is similar to many of the Personal Video Recorders (PVR) on the market today because when you turn off a PVR, it is really just going into a low-power state. This feature, once Update Rollup 2 has been installed, can be found in your Power Options in the Control Panel. You should see a tab, similar to the picture above, that says Away.
Microsoft has also thrown in some other updates to Media Center: DVD-burning improvements, DVD changer support, support for 4 tuners, and support for Windows Media Center Extender for Xbox 360. Many of these new features were highly requested by Windows Media Center users, especially the 4 tuner support, so that people could ditch their PVRs and make the move to Media Center.