I'm very impressed with this lens. Before I bought it, I read reviews on various websites, some saying it was brilliant, some saying it wasn't very sharp, too big, too heavy etc.I took the plunge and bought one and haven't regretted it. I've used this on d40 and d300 bodies and it works superbly on both.
The autofocus is very fast, quiet and accurate. The VRII system is also very impressive allowing very slow shutter speeds - I've had sharp, handheld images at 1/30 sec at 300mm which would be completely impossible without it. As for the size and weight, for a lens with a maximum focal length of 300mm with a built in focusing motor and an optical stabilisation system it's not really a problem (the canon equivalent is the same size but 100g lighter). The build is also fairly solid with smooth zoom and focus rings. Mine has had it's share of knocks and bumps as well as being caught in rain and has carried on unaffected (note that the lens mount has a seal round it, helping to stop rain from seeping between camera and lens). I can't really complain about sharpness either, the only times I think the image is a bit soft is at the longer focal lengths which could as easily be due to bad panning technique, relying on the autofocus too much in poor light etc....
For a 300 mm lens at this price, it's got genuinely useful features, it's compact, not too heavy and impressively sharp - Fantastic value!