I own both a USPf and USPc in .40. The USPf I bought in 1994 and have put over 20,000 rounds thru (USPSA shooting, range time, etc.). It has never had one FTF, FTE, or any other malfunction, regardless of frequency of cleaning or type of ammo. My USPc I bought a year ago as a CCW and have put over 1500 rounds thru, also without any malfunctions.
Having said all that, and despite being an ardent HK fan/supporter, I always dissassemble, lube, functions check and run about 500 rounds of various type ammo thru any weapon, new or used, that I have purchased prior to feeling comfortable with it. That is the prudent, common sense, and responsible thing for any firearms owner to do, since without doing that you are accepting responsibility as the firearm operator without checking your equipment prior to use - would you want a bus driver, airline pilot, etc. doing that? As a still serving Army Jumpmaster and combat veteran (and very anal about the details of things), I would not, and as long as HK firearms are built by human beings, then the old saying, to err is human applies - even if only rarely as is the case with HK firearms.
BTW, the US border patrol now carries USPc in .40...as do some of our SOF folks..