The custom Colt A4gery (AR15) I had Wild West Guns build for me only has about 8,500 rounds through it at this point. I've replaced the action spring just because it seems like I should from time to time. Should probably pick up an extractor for the inevitable...
My kalashnikovs... who knows? A lot. Many times more rounds than I've fired through my current AR, but they have yet to break (knock on wood).
I don't shoot the same volume of ammunition through my handguns on average, but I shot my Hi-Power until the extractor went. Something like 10,000 rounds, but the garbage ammo I was shooting when it broke may have been responsible.
The barrel link on my cheapy Brazillian Springfield 1911A1 broke at something in the neighborhood of 7,000 rounds. That was an ugly malfunction, it locked the gun up completely. The worst part was you could retract the slide just enough to see brass in the chamber, and I was unsure if it was a live round or spent brass in there. The gunsmith just loved that.
That's all I can type at the moment, maybe I'll think of some more later.