Funny this comes up now. Sebastian just wrote about ammo rotation and SayUncle commented upon it.
You see, yesterday while working the deer lease it eventually started to rain pretty hard. We were at the back of the property, too far from camp (and my rain coat) and so we just kept working. I was soaked to the bone. I did remember to leave my iPhone in a dry place and I also left my spare magazine there. However, given the amount of water I took on, on the drive home I made the decision to rotate out all of my carry ammo, even tho I just did it a few weeks ago (the normal 6 month rotation). My wallet sighs, but I’d rather have the assurance of “known good” ammo. Yes I’m pretty sure the ammo that was in the gun will still go bang, but my life is worth the assurance. I’m even going to change the rounds in the spare magazine because while they didn’t get the soaking, they probably took on some rain during the course of the day. I’ll shoot the “wet” ammo next time I go to the range to practice.
Sebastian hit upon the key thing:
Ammo does last a long time, on the shelf. But carry ammo is not ammo that’s sitting in a safe or a foot locker, in its factory container, often sealed. You’re carrying it around with you. You sweat, you extrude oils, salts and various proteins, which get on the ammo when you handle it, and are on the dust particles your skin and clothes give off and end up in your gun. Every time you chamber and unload, you’re putting stress on the ammunition components.
So, to rotate or not? Everyone has their take on it. I do rotate my carry ammo on a regular basis (about every 6 months) because I’d rather be safe than sorry. The ammo loaded in a home-defense gun? Not so much, because it’s sitting in my nice, climate controlled house; eventually it will be rotated, but I don’t feel the need to do it as often.
Stuff From Hsoi 
I don’t really have a schedule. When I feel like it needs to be shot up, I shoot it.
Other than repeated chamberings, I think the risks are totally overblown. It’s probably ammo manufacturer propaganda. :)-~
I do rotate in the mag so that number of chamberings is fairly balanced per round.
On a related note, something thing I do, that not everyone does but probably should, is that I inspect each new carry round. I get my case gauge out and check that it fits. I also check that each primer is seated correctly, and inspect the bullet for nicks or other deformations.
I did notice setback on one of my rounds once, due to repeated chamberings. It is certainly worthwhile to always check this stuff.
I don’t have a schedule either, but I check my ammunition weekly. For my semi autos, I empty the magazines, checking the follower, lips, and mag body for any issues. Then I check the ammo, lining the cartridges up and inspecting for setback and deformities in the bullets (hollow points are fragile, I’ve found), then I check the rims and the primers for any discoloration or corrosion. If they are discolored, I clean with a clean, lint and chemical free cloth. If there is anything questionable, the ammo goes in the random box of range ammo and the rounds are replaced. Belt revolvers get the same inspection as semi-autos with the speed loaders getting checked for bullet deformation more often (when you pocket carry speed loaders, the rounds sometimes bang around, because I carry two SLs to a pocket).
For revolvers that are pocket carried the ammo is checked daily during carry. I carry ONLY Remington Nickel Cased 158-grain LHP, because the lead is good and doesn’t deform, there is not jacket to damage (I’ve damaged jackets on Gold Dots), and the bright nickel cases do not tarnish. Also, Remington seals primers with some kind of red sealant which allows easy confirmation that everything looks good.
I rotate my ammo when I feel it needs it. For instance, I just rotated the carry ammo in my 9mm, it had been loaded with that ammo since Feb. The reason I rotated, was because I FINALLY found some 124-grain Gold Dots at a reasonable price.
-Rob