Dil Roberts Photography
This must be one of the best bargains on the market right now for m4/3 users. Very accurate an produces very nice images. I think most people will have trouble deciding between this and the 100-300. I don't think it will make a difference to most people. The 45-200 is a bit smaller than the 100-300 and the 100-300 has the longer reach. It depends on what you want from a lens. Once you know that, you just buy the one that fits the bill.

Panasonic 45-200 f4-5.6 OIS on a G1