Most of my bird shots are taken wide open, yes.
I've had this lens for quite a few years now but don't get out with it very often so am quite inexperienced.... which is why I have never ruled out user error in my troubles.
I've mostly used the lens wide open to try and get the shutter speed high (and ISO low). Next time I go out (hopefully Friday) I will try and use F8 with a higher ISO to see how I go. I will also use live-view as I think I get better focus with that.
I have been recently been thinking of selling the lens and upgrading to a VR version, but didn't want to based upon the fact that I wasn't sure if the lens had a problem and didn't want to sell anyone a lemon. I'll keep testing (and saving) and see how I go.
Thank you so much for your help! If I can start to get some better results with this lens stopped down you will have made me a very happy man!
EDIT: Looking back over my past images that I have deemed 'acceptable' with this lens would suggest that stopping down does indeed help... most (but not all) of them were taken at smaller apertures.
Paul