Been using Pentax for last 5 years or so and everything in my portfolio is shot with Pentax. Currently shoot with Pentax K-5 and my absolute fav lens is the 50-135. Amazingly sharp, versatile, well built, and easy to carry around all day. I actually wore mine out and it is away for repairs right now...thankfully Pentax had the prices back to where they should be and I was able to pick up another at the fantstic $750 price. Actually bought e DA 40mm pancake after seeing Benjamin using it on a K20D for a Vogue shoot once. Such a tiny little gem of a lens!
Of course there are definitely some things I wish Pentax had that competition has but I am pleased. My wish list includes: full frame, a Pentax 70-200 f/2.8, new and better flash, dual card slots, and flash sync at 1/250