Yes, it is a bit soft from about 280-300mm on a DX camera, e.g. a D40x.
However, I find that it is actually less of a problem on an FX such as a D700. The lens seems to be well suited to the larger format.
I had planned to sell my 70-300VR when I got the D700, but kept it when I saw the results.
This is a very versatile lens all round.
Ed
Curious how a "cheap" lens can get better with a more expensive body - who would have thought!
It's pixel density. The sensor out resolves the glass in the 10+MP DX cameras.