I picked up the 20" barreled one,haven't shot it yet.
I don't own one personally, but a couple guys at the club do. (One in 7.62, one in 5.56)
The biggest issue I saw was reliability. In both guns feed jams were common, about once every other mag. I don't know each owners cleaning/lubing routine, but I can say that reliability has been an achillies heel for keltec for a while now, which is a pity because I think Kel-tec is a really innovative company with some really neat ideas.
IMHO, keltec tends to field a design and use their customer base to reliability test it.