the problem is that it sounds like most of you are still running MS Windows 4.x (95, 98, ME, and NT). I used to shut down every night when running 98, but now that I run win 2k I leave it running 24/7/365, I just have the monitors (I have 2 of them for this one system) automatically power-down when I'm not using it, I used to have it than go into hibernate if I left it Idle for more than an hour, but I've been running seti lately, so I dont shut it down anymore.
I also have a red hat server that I keep running 24/7/365 as a server (when I have a site running, it's HD died though, so it's not running at all until I take the time to get it a new one)
If you have a stable OS (just about anything other than win 95,98, or me) than your computer should easily be able to run for a week + inbetween reboots.