Question: I have many Linux servers (SUSE 9 &10) used to run web services that provide data to large calculation grids. Recently we have had some difficult to explain outages (i.e. hardware and software logs are not showing any obvious errors) and we are starting to wonder whether the long uptime (typically 200-300 days) is the issue. Given that these servers are heavily utilised, should I consider a regular reboot cycle?

Answer: 
Not really required, linux memory handling is excellent. But if you're having uptimes of that length you're probably running kernels that have known vulnerabilities - you might want to watch that.
Depends on the tasks running on the server. For some virtual servers we often use reboot instead of i.e. apachectl restart and it just takes 5-10 seconds longer. But some heavy loaded machines are rebooted several times per year with a whole admin crew monitoring the process.