I still remember the days of servers as pets, rather than cattle, and I was harping about server uptime. A wizened server admin piped in and said he rebooted his servers once a week. Said, if you do it any less frequently, then the odds of catching an error causing change while the person who made said change (possibly himself) is still around and can remember what they did go down precipitously. So, to avoid headaches and potential downtime when it mattered, he would just take servers out of rotation and reboot them, and make sure they came back online.

So true. We have one older, rather large machine in a data center that's been up for.. (checks uptime): 963 days. It has IPMI but at some point something stopped working and now we have to physically go to the data center to restart it. And since we use it every day we can't really afford to lose access to it.