I took some shots on Sunday with my GH2 and my recently acquired Panasonic Leica 45mm f/2.8 macro lens. I was staggered by the sharpness of this lens.
I have been thinking about using it as a replacement for my Olympus 50mm f/2 macro four thirds lens. Particularly since the GH2 hasn't really improved things in terms of AF for that lens. Before coming to a final decision I decided to do a comparison test between the two.
There is a larger version of this if you click through to flickr.
What I found is that I couldn't tell the difference between the lenses. Apart from a slightly warmer colour balance on the Panasonic lens, they were almost identical. Certainly in terms of sharpness. Both are excellent, top quality lenses. The Panasonic offers fast AF on m4/3, the Olympus a faster f/2 aperture. Certainly my test showed there is no advantage in terms of image quality from the Olympus on m4/3.
Whether I can part with the Olympus I don't know. Its a great lens, though difficult to work with. Whether I continue with four thirds with either my Panasonic L10 or even an Olympus E-5 which I'm still considering, I haven't yet decided. Very much a heart versus head thing, as four thirds seems to be a dying system, and offers me virtually no advantage over what else I use. I just love those four thirds lenses, and a four thirds camera would enable me to use them with full-speed AF. Whether I continue with this or sell all my four thirds gear is open to question at the moment.