I have one and like it a lot. The only problem I've had with it is that with some magazines the bolt hold open device will ride up prematurely and hold the bolt open when you still have a round or two in the magazine. To "fix" the problem, I bent it slightly back and now it doesn't accidentally hold open before the mags are empty, but instead will sometimes not hold the bolt open after the last round on other mags. It all seems to be caused be differences in the toleranaces of various aftermarket mags. Over all, it's not a big deal though, and I like the rifle just fine.
That being said, I have to agree with the poster above... I also have a Kel-Tec Sub 2000, and I'll have to say that the 2000 is lighter and slightly more accurate than the ruger, and so far hasn't had _any_ malfunctions.
I've owned both of these for several years now, and enjoy them both. I think you'll be happy with either of them. YMMV, of course.
- edited to add that my 2000 uses the beretta mags, and I've found that I can easily modify my ruger P-Series mags to work in both it and the ruger by dremeling a slot into the side for the beretta style mag catch.