1 week, no problem. 1 month no problem. 100 years no problem.
I have left my computer on for 10 months and 2 years prior to that. I moved about 10 months ago so I had to shut it off. I reboot when I update windows and virus software, but I still leave the power on.
My everyday computer I turn off just mostly because of the noise level by the fans.
My other computer acts as my file and web server, so I have a special room for it. Noise not a factor on that one.
Soyo Dragon Ultra Platinum Edition powered by a P4 3.06GHz w/HT @ 533FSB
ATI Radeon X800Pro 256DDR <---Yeah!!! I finally got it!!!
1024MB PC3200, Creative Audigy LS, 2 x 40GB = 80GB RAID 0
Windows XP Pro, DOOM 3, CS, UT2004, BF1942 RtoR, CNC Generals
Finished Half-Life 2!!!!!!!!!!