I was using these two lenses today, the Panasonic 14mm f/2.5 on the GH2 and the Pentax 21mm f/3.2 on the K-5.
I briefly tested them against one another for sharpness and found them to be very much the equal of one another throughout the frame. Both have very strong central sharpness and adequate peripheral sharpness. With obsessive pixel peeping, the Panasonic was a bit sharper (and noisier) everywhere, but a little extra sharpening applied to the Pentax files (to make up for the slightly stronger AA filter of the Pentax) leveled things.
Here's a sample 100% center crop at f/4, Panasonic on the left (tripod, self-timer, aperture priority autoexposure, shot in triplicate, processed with default Lightroom 3.3 sharpening and NR plus default Nik Output Sharpening which maximizes detail but also increases noise and artifact):
Edge crop from the same image:
The Panasonic performance at f/2.5 was on par with the Pentax at f/3.2 (data not shown).
Operationally, I find the Panasonic superior in most ways. The Lumix is much quieter, much faster to focus, is smaller, and lighter. In contrast to the Pentax, the Panasonic doesn't extend during focusing, takes a conventional filter without removing the hood, and doesn't exhibit focus ring movement during autofocus. The Pentax feels more precious (standard Pentax Limited metal build/finish) and is superior for zone focusing due to mechanically-linked manual focus (focus by wire with the Panasonic) and distance scale. In addition, the Pentax lens is stabilized on the K-5, whereas the Panasonic lens is not stabilized on the GH2.
My strong bokeh preference was for the Panasonic. The two lenses provide a similar amount of background blur when used at their respective max apertures and min focus distances (which are very similar), but the Pentax OOF rendering wide open is very harsh relative to that of the Panasonic. Here's an bokeh sample image shot with the Panasonic:
I took a similar shot with the Pentax and will show two representative 100% crops. In each case, the Panasonic crop is on the left: