I bought an M&P 15-22 A1 Carbine (Product: Model M&P15-22 - A1 Style Comp) in December 2012 on a lark and love it. It is one fine little .22LR. I have installed a Geissele SSA-E trigger in it and a vertical MagPul grip on the handguard. Love this little .22 AR.
Late last spring, I vacillated between two .22 pistols; a Ruger Mark III 22/45 LITE and an M&P 22. I bought the Ruger and after taking it to the range, just wasn't all that enamored with it. I do have a Ruger Mark III 22/45 Hunter 5.5" stainless and like that one. I have changed out the sights and installed a hammer bushing to remove the magazine disconnect safety and smooth out the trigger. That one's a keeper. As for the LITE, I kept going back in my mind to that M&P 22. So last fall, I happened to be in my favorite LGS and they had one in stock. I handled it and bought it on the spot... without even firing it. Sold my LITE and at the range was I surprised. That M&P 22 is probably the best .22 pistol I have ever owned. Not the most accurate, but the most fun to shoot.... and the easiest to clean.
I do buy guns on a lark out of nowhere on occasion. More often than not, they turn out to be winners but a few times I have been disappointed. The M&P 15-22 A1 Carbine is just a sheer joy to shoot. A solid keeper for sure.