With a Glock, I don't worry about going a long distance between cleanings, so long as the gun has some lube in it. Most other regular carry guns I'll clean at least every few hundred rounds, again making sure they're appropriately lubed. I like to bore brush revolver chambers every 50 rounds or so just to insure clean gravity drop of fresh cartridges from speedloaders.
Personally, I don't really trust a gun 'til I've got a couple hundred of the carry loads through it, and some of my colleagues think I'm too easy on that. I'll often carry a gun I'm testing for a magazine -- if it's a carry piece, that's part of the testing parameters -- and it's not always practical to do the 200 rounds of the chosen carry load with a temporary gun. I'll run at least 50 carry loads through before I put it on, though, and will be sure to carry a backup.
If the manufacturer changes the bullet, I'll want another couple hundred through the gun before really trusting the updated ammo. If it's just a different lot of the same "recipe," I personally don't feel that's necessary. However, I do make a point of always having the same lot of ammo in the same gun, in case I need to track back for evidentiary testing for gunshot residue.