I believe Martyarty's Kingfisher shots are taken using the combo you're looking at.
I use the 150-500, but with a 40d, so not nearly the crop-ability. I did have to return the first version, due to focussing issues, but the 2nd one is much better & sharper too.
It's obviously a lens which requires some compromise, ie. in low light, but OS works very well & with a 7d you'll hopefully be able to raise the iso without worrying too much. I'm almost certainly going to upgrade to a 7d myself for this very reason & better af for moving objects.
I've also gone through a bit of a learning curve, but I guess that would have been the case with any lens at 500mm. The lens is definately able to produce the goods & I'm getting more keepers as I improve with my use of it.
There's also a very large 150-500 thread on POTN, you'll find quite a lot of poor pics on there but some very good stuff too, particularly a guy called "gabezales" (I think), he uses a 7d too.
I have to say I was shocked when I heard there was
another photography forum
, but I checked..........& it's true!