I just leave mine in sleep (standby). Sometimes if I get angry at the computer I'll just force shutdown (hold the power button in) and leave it alone. I reboot it if it goes crazy (USBs stop working, sluggish, etc)
My server computer is left running 24/7 - unless it has a power failure. (Storm, blackout, etc etc)
Funny, both my XP 64 system and main Debian server have been up for about 19 days now. Didn't realize I rebooted them around the same time (had to increase HugePages for E, replaced busted RAM on main machine).
Other Debian machine has been up 83 days. My XP Laptop has only been up for 3 days now.
Turn it on in the morning around 10am after visiting my old man across town for a cup of coffee. Turn it off around 2-3am after a full day of work, and then leave it on evening cause i usually forget to turn it off, and then actually turn it off at that 2-3am mark before i go to sleep. But I work @ home so there's a reason I leave it on all day.
I barley ever shut mine down. It's porbably been months since I last did it. I Lock it or put it to sleep when I'm not using it, and Hibernate it when I put it away.
Once i get windows 7 instead of vista i might turn it off at nights but my pc takes like 10 minutes to turn on and i cant work out the problem, i have formatted my HD and then put everything on a external HD, hmm...
Funny. I never really payed much attention to it but now that you say something it probably isnt a good idea to leave my computer on all the time, if not for the life of the computer then for the energy costs lol
At least I restart it every couple weeks or so for updates and such, gives it a chance to refresh.