Are you rebooting because you need to, or for some other reason?
I've only run mine for 2-3 months because I shut it down when I'll be away for a longer stretch of time (usually a 4-5 day span is enough for me to shut it down). I also only am running the server when I'm at school, because we have a small NAS box at home that has the same media library and there's no point in having two boxes serving the same content in a small household.
In the time I've used my server, the only stability problems I ever encountered were related to a flaky power supply.