I love extreme lenses which is why I couldn't resist obtaining the new Lumix 100-300 f4-5.6.
Here is my take on the lens. Nicely built in typical Pansonic quality plastic style. Less impressed with the focus throw on my copy which is stiff. Maybe it will loosen up with use (I hope). It is a big lens but not as big as, say, the equivalent focal length or even half the zoom focal length on any other system I know of. In fact, you could say the promise of m4/3rds is finally realised with this sort of lens in terms of size. Comes with a nice reversible lens hood and a soft case and caps.
Obviously, it is a hard lens to get a sharp shot from at maximum. The problem is the inevitable shake and the need for high speed. I really doubt the OIS is much use and in fact the manual even hints that you might want to turn it off at high magnification.
As a result, this means operating at high iso and unfortunately my GF-1 loses a lot of definition above iso800. I can recover some of this because I shoot raw and the raw settings tend to be soft and noisy. However, when shooting birds, for example, this leads to a loss of detail.
In typical Panasonic style the lens is capable of sharp, colourful pictures, though I feel it will take some time and practise to get the best out of this lens. And possibly a GH-2 if the improvements to high iso definition that I've seen in samples really are there.
The full size jpegs are at my Flickr stream if you feel the need to pixel peep. All pictures have minimal to no post processing.
iso640 f7.1 300mm 1/500
iso1250 f5.6 234mm 1/250 - pleasing bokeh?
iso160 f7.1 120mm 1/200
iso200 f5.0 125mm 1/200
iso640 f5.6 300mm 1/800