I have not seen any white paper from Microsoft regarding best practices of a reboot schedule.

In our organization, we only reboot the servers when patches are applied or (rarely) when hardware fails and necessitates downtime.

To enable that long term reliability, only the bare minimum services and software are installed on the dedicated SQL servers and the third-party driver versions are chosen carefully after lab testing. The end result was very reliable systems and the ability to convince management that a reboot schedule was not only unnecessary, but created downtime when the goal is to reduce it.

David R Buckingham, MCDBA,MCSA,MCP

SQL Database Administrator

WebMD Corporation