I'm sure it'll be a good lens for its purpose, Steve. I was, of course, speaking from a personal point of view. I have a Canon DSLR with a Sigma 400mm Apo/Macro lens which is ideal where you want to get a shot of a butterfly/dragonfly in less than ideal situations - for instance, when time is at a premium on holiday (wife watching impatiently!).
When holidaying in Europe the weather is usually sunny enough to assure fast shutter-speeds so the long focal length isn't a big problem for hand-holding but lugging it around all day in hot climates can get a bit tiring after a few hours. The weight-saving and compact size of a similar micro 4/3rds system would be really useful to me in these circumstances.
My 400mm gives a 'crop-factor' focal-length of just over 600mm on my Canon and the minimum focus distance of 1.6m gives a macro ratio of 1:3 on full frame which means slightly better than 1:2 and the lens gives high-quality images at this distance.
Of course, I'm not expecting Olympus to bring out a 300mm prime of a similar spec to my 400mm so I have to accept some compromises. The smaller sensor + the (probably) lower-quality image + the closer focus distance makes three compromises and the fact that I'd have to crop the image even more to get a similar-size image of the insect is probably one compromise too far.
I really like the concept of the micro 4/3rds system and I think it's what the original 4/3rds system ought to have been all along, but there's got to be a wide range of lenses/ accessories to go with it or it'll just get swamped by the 'big boys' when they finally get their mirrorless cameras out there.