I have broken or outlived the following during its life: (not counting routine maintenance replacement)
2 Strikers (both broke, gun would have light strikes and the 1st time I could not shoot my Frangible ammo at work ... was a real big pain in the ass)
2 Extractors (it came with a really bad one, but my buddy from S&W replaced it for me, then did it again later. I replaced it a 3rd time with an Apex Extractor I had to fit it a little, and its been great since)
1 Slide Stop Lever (the left side broke off when I used it to send the slide home at around 60Kish)
3 Recoil Springs (I switched to a non captured system and used to replace the unit every 5k rounds, but now I replace the spring only every time it gets 1/2 inch smaller then original (and if it comes to that within a year they replace it for you for free!) using an
ISMI #15 recoil spring with a stainless steel guide rod. I had some issues when I first started shooting the gun, but when I went on a replacement schedule I didn't have the issue anymore. Switching to non captured saved me good $$)
5-10? Magazine Springs. I have no idea how many rounds my magazines feed (I wish I had kept track, but its too late). I just use a simple guide and at the end of my 1st year my magazines would not feed properly. I found out that my magazine springs where 70% the size of the brand new magazine springs. Once my springs go down to 80% I replace them now. Its recommended every 5 thousand rounds per magazine, but I just don't have a way to tell unless i get super OCD on those magazines.
I do NOT criticize the gun. At my former job in the Marine Corps we would break 1 or 2 M9s every week. (Our students would put 20k+ rounds through 12 guns in a period of 1 week and the same guns would go through that next week) Usually it was the locking block that broke. Any firearm that you put a shitload of rounds through are going to break. A very large majority of the rounds I put through my 9L were A363. Very hot ammo. About 2 years ago I started following the maintenance guide for my M&P and I don't have problems =). A weapon is a mechanical device, and last time I check I can't drive my car 100,000 miles without an oil change and maintenance.
I have sent the gun off for maintenance off in the past and had no issues .. but its probably been 2 years since I have done it.