I'm just curious how many keep track of the amount of ammo you put through each of your guns?
If so, why? Is a handgun only good for x amount of rounds?
On my target guns, yes. Stainless barrels are perhaps more accurate but don't last as long as say, a 4150V melonited (or even chrome lined) barrel out of an AR. I'll keep track of my rounds out of my target bolt guns as well - usually you'll notice your groups getting slightly bigger after ~5k rounds (or less, or more, depending on your caliber/load/etc.), which will continue to get worse until you replace the barrel. DOPE books are useful for that.
For my range/plinking guns, not so much. My 'fun' AR that I putz around with, or teach people to shoot with, I don't worry about...I just replace parts when they show signs of wear. I'm not as concerned with a possible failure to feed/extract, slight loss of accuracy, etc.