Addendum:
I own the 70-300mm for some time now (only on my E-510, now in my E-30) and am still very happy with it. What I have not mentioned above is possible with the lens magnification ratio of 1: 2 - the same size as the 50mm Macro lens and you can make (a steady hand vorrausgesetzt) at 300mm focal length with the shortest possible distance to the subject really impressive macro shots. For someone who is generally interested in nature and like all animal photographed whatever comes before the lens, which saves a lot of 70-300mm lens changes, because if bird, squirrel or hoverfly - with the 70-300mm you get them all; -).