(Fortunately,) My experience with Ruger's .22 resembles that of poster nitesite. I own a the "competition model" KMK-678GC with 6/8" slap sided barrel that I shoot at the range almost every weekend. Although, I would prefer a somewhat nicer trigger characteristic I refrained from tinkering with it as it's otherwise a great gun in every respect - accurate, reliable and dependable. I've even shoot my Ruger at 100 Meters with a handgun scope mounted on it and it was a lotta fun!
I also use it for formal target competition of German shooting association BDS (where many competitors enter with much more expensive European rimfire match pistols like the Walther GSP, Hämmerli 208 and 280, Feinwerbau's AW93, the old ERMA ESP-85A or whatever) and I do well with it.
One thing I especially like is that the Ruger (and the S&W M41 that I likewise respect, for that matter) still looks like "real" a pistol, unlike most of the competition that resemble strange-looking shooting machines.
I admit that nowadays I'd probably opt for the S&W M41 (I've already shot the 7", 5 1/2" variant and a shortened special order gun with red-dot sight), because it has a better trigger. Still, the Ruger serves my needs perfectly, so I can't rationalize a switch.
I am sorry for the guys having trouble with their .22 Ruger MK pistols. Seems there's something wrong mechanically on some specimen.