I have heard very mixed reports..
Some people say the focus is as fast as the F2.8, others say not..
It is generally accepted that the tripod mount is pretty shoddy (although it can be replaced).
The optics are meant to be superb though by all accounts..
There's a review here -
http://www.bythom.com/300AFSlens.htm
EDIT - another review here with an 'interesting' solution to the tripod mount! -
http://www.naturfotograf.com/AFS300_test_images.html
This is a good resource for NIkon lens reviews -
http://www.nikonlinks.com/equipment_main.htm