I love mine for birds, but it seems every time I even look at the lens with the idea of mounting it, every bird in the county flies away. I've gotten a few specks of BIF that suggest it would be nice and sharp if I ever got within a half mile, and I got a nice mourning dove butt, but so far I feel like a one-man ecological disaster.
I have not used this as much as I'd like to, since winter in Vermont is pretty poor for it, but my initial impression is that it's nice and sharp, the AF is decent but not lightning fast, and the VR is superb.