The only Kimber MIM parts I have seen break are the pictures that have been posted on this board. Neither mine, nor any of the dozen or so owned by friends I shoot with regularly has ever had a problem. Same with the plastic MSH. Now I actually intend to replace mine with an arched housing with the lanyard loop when I happen across one, but I have never heard of a plastic one breaking.
My personal extensive experience is as follows.
In the army we had 87 WWII frankenguns of various manufacture and origins. I only shot them once, I don't recall any malfunctions of any kind. In the spring of 1992 we traded them out for new-in-cosmoline Berettas and I wept. I stole a handful of the G.I. magazines and I had all kinds of trouble with them.
I traded a guitar to a friend of mine for a Auto Ordnance 1911 which would have been manufactured around the early 90s. It was a nightmare. Everything about it was terrible. The sights, the slide, the trigger, and to top it off, the front sight popped out two days after the front sight on my new Sigma did the same thing. I got rid of both of them.
I bought a new Colt 1991 A1 in about 1995. Very vanilla and spartan. I liked it just fine, but I don't recall anything special about how well it functioned. It was much like the G.I. ones I had used in the army. I left the country for a while and wound up selling it.
I bought a used Para Ordnance P-12. Again, not bad, but pretty unremarkable. I went through a phase where I carried a Beretta, a Sig, a Glock, etc, and I came back to a Kimber 1911. I shot it, and all of the function was so fluid and perfect, I suddenly felt like it was what I had been looking for all this time. It was how I WISHED all of those other 1911s had worked. I let all of my friends shoot it, even those who weren't fans of the 1911 or .45s in general. They ALL loved it, several bought them, and most of my friends who carry now carry Kimber 1911s.
My dad asked me for suggestions for a 1911 and wound up buying a Springfield Armory Mil-Spec, and as was mentioned above, he will need to get the slide machined if he was a selection of sights. A good friend of mine went in on a group buy from Para Ordnance for some wide-frame 1911s with custom colors and graphics dedicated to a particular military unit. When he got his, the cavity under the bushing, where the plug sits was squeezed so out-of-spec that the plug wouldn't come out. He had to send it back to the factory to get it re-shaped. Both of them said they really wish they had just bought a Kimber.
Here's the thing. Kimber sells several TIMES more units than the next 1911 manufacturer. (BATFE posts these statistics if you want to check.) When you sell many more TIMES the number as your competitors, there may well be a higher percieved number of malfunctions. Added to this, on boards like this, NEGATIVE experiences with a particular gun get much more bandwidth than POSITIVE experiences. ("I bought a new gun this weekend, I took it to the range, I shot it, cleaned it, and took it home." is pretty boring.) Even if there is a higher NUMBER of problems, it doesn't mean there is a higher RATE or likelihood of problems than another manufacturer.
In all fairness, I try to look at all options in a given price range when I buy a gun. If I had to replace my Kimber tomorrow, I might look at a STI Spartan, a Dan Wesson, or some similar ones. But I have never had any more success between me or my friends with any brand or model than with Kimber 1911s. If the MIM parts REALLY give you the willies that much, they are all easily and cheaply replaced. (I haven't bother or worried about it in over 10,000 rounds.)