Also reboots are not necessary if your OS is stable. If you're using Windows XP (with no spyware, etc) or Linux then it'll be stable enough to run for months or years with no problems.
I shut my computer off every night. I cant sleep with howling of the fans it drives me nuts. I have left it on for a few days though to download stuff. But usually it goes off when im not going to be home for a while or im sleeping.
