It's ace. Coupled with the D300s, it's amazing. Super fast AF, brilliant IQ, sharp thoughout the zoom range. My only complaints are that it is a rather large, bulky lens so carrying it around for an extended period of time can be a chore, and it seems to flare when pointed at direct light sources (not too much but more than I expected). The stiff zoom ring doesn't help much either though at least it doesn't creep.
When doing my research thought, it seemed one of the biggest optical issues people have with this lens is the barrel distortion and I must say, it's hardly as prevalent as people make it out to be. That said, it depends on what you're shooting at. I purchased this lens for use outdoors (weather sealing and solid build come into their own here) so such effects are going to be more of a concern when shooting buildings and the likes.