Several at our gun club have them. No problems thus far, of any major nature. Can't say as much for the Colt 22 rimfire AR clone.
One guy did have a minor problem with his S&W, but it was resolved quickly, can't recall right now, what it was though? Do know he was the first person I know that got one about a year ago and it's been heavily-used.
So then your talking about the S&W M&P 15-22 and not the S&W M&P 22. Sorry for the confusion.
I've owned 2, loved both. Would love to get a third. (In case your wondering why I sold them, it was to furnish other purchases - 5.56 AR & 7.62 AK. I figured the .22 wasn't necessary). They sure are a heck of a lot of fun.