Sometimes I notice that my website is down for 5-10 min. I've contacted the hosting support but they told me that the outages are due to server reboots that happen on average once a day, and that this is normal.
I have a pristine WIN2K box and a couple of apps that if left running a couple of days will make the box almost unusable. If you want to use the box with those apps you have to reboot every now and then. Keep those apps off and you never need rebooting.
Doesn't matter, I only put important stuff on Linux anyway ;)