Absolutely no reliability issues with my Kimber Ultra Carry.
I've shot plenty of my H&G 68 hard cast lead SWC reloads ("standard" IPSC load, but probably one of the toughest rounds to feed, my Taurus PT945 won't feed 'em) Wolf FMJ, Win "white box" FMJ, 230 gr Hydrashoks, and 230 gr Golden Sabers. I also had a few of the old CCI Lawman 200gr JHP "flying ashtray" that is also considered a tough to feed round. No problems.
I did change the extractor to a mil spec spring steel one, soon after I got the gun because what came with it had very little tension, and I had an extra sitting around. The original gave no problems but I though it was a cast or MIM part. Someone here claims Kimber only uses machined, in any case it was obviously weak and not the best quality part in the gun. Too much tension will lead to feed failures, too little makes for extraction/ejection problems, but its not hard to adjust a properly made mil spec extractor if it needs it. Just made me feel better to swap it, not sure it was really necessary.
--wally.