I did my own experiment on canned food, and it looks like 2 years is a good average. I recently opened some vegetables that were from May 2008 and they were fine. The beans looked like they absorbed most of the sauce they were packed in and were a little pasty, but didn't go bad.

I heard the same thing Sniper did about Spam.
I've eaten 10 year old MRE's, and they were fine.

The best thing to do is what they recommend at emergencyessentials.com (or beprepared.com), make all of your food storage part of your regular diet so it always gets rotated.