Just got my 70-200L. I have been putting through the loops.
This was taken hand held with my 50D (crop body) and a 2x extender. I know people say don't waste time with the extenders and they only degrade the image. I am quite pleased with the results when shot properly. I can see the extender will get me some shots I would have never been able to get without it.
F5.6, 1/1250sec., iso 1000, 342mm.