Own both a K10D and a K5II, both of which have grips. K10D has a copy, but the K5II has an original Pentax one. Couldn't consider owning a camera without a grip. Had a Canon T90 years ago - ergonomics were brilliant. K5-II with a grip is the nearest I've come to it. It just balances things so nicely, even with just a 50/1.4 lens on it. Put a 60-250 f4 and it just handles sooo much better. I also like the idea of the extra battery and card being in there. Also, it is useful to have AA batteries as an option.

Nearly bought a K30...but it doesn't take a grip.
Love the K5-II though.