You are using of course LTS for your servers, right? Because otherwise it would be stupid... So, is 3 years support not enough for you?
Actually, Ubuntu LTS server is five years. http://en.wikipedia.org/wiki/Ubuntu_(operating_system) In fact, 6.06LTS server support is just wrapping up this June. Desktop versions of LTS are three years.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (6) Them bats is smart; they use radar.