We are actually replacing our current file server with a new one. The new one is a more powerful machine and has back up power supply, RAID hard drives, etc. Basically if the current one died the site would be f'ed until it was fixed. So we've been lucky so far. Last week the database server, which is a similar machine, blew a hard drive, but the site kept on going because it also has a RAID hard drive system.
Also our current file server has a 100mbps connection and the new one has a 1gbps connection. The current file server seems to be causing our webservers to reset. This causes the site to lag and pause at times. We're hoping this goes away once the new file server is up.