I've had two failures to feed in my KK date code (year 2000) USP Compact .40, both were bum rounds where the bullet was seated crooked. i did break my firing pin somewhere around 5,000 rounds after A LOT of dry firing. i was told there was a batch of firing pins that weren't properly heat treated and the problem has since been corrected. i sent my pistol in to them and had it back within a week, repaired free of charge. the service was plenty satisfactory to me. at about 7,000 rounds, the little clip that retains the recoil spring on the guide rod broke. didn't affect function at all, just made it a little more difficult to reassemble after stripping. i called HK and they sent me a three pack of them free of charge. had them in a couple days. i'm now at about 12,000 rounds through my gun. it still rides on my hip just like it has every day for the past 7 years. i wouldn't trade it for anything. when i clean it after a range trip, the barrel looks brand spankin' new inside. you would never know its even been fired. the steel that its made of is so hard that i tried to polish the feedramp (out of boredom, not necessity) and my results were just so-so because polishing compound isn't nearly abrasive enough to remove any metal, even with the dremmel on the 30,000 rpm setting.
it feels like my recoil spring may be getting a tad weaker these days. i may replace it soon just for peace of mind.
i certainly have no regrets about buying this gun. i'd recommend them to anyone. sure they're pricey, but worth every penny if you ask me. its not perfect. its a mechanical thing after all. some things are going to wear out and/or break on it sooner or later. if the little clip is the worst that happens, i'll consider myself pretty lucky.
Bobby