Sigma 70-200mm F2.8 HSM II

I'm a poor student who wants to buy a telephoto zoom, mainly for portraits. All the research indicates that the new Sigma 70-200mm F2.8 is the logical choice. It seems like the sigma is just the less-sharp-no-VR version of the nikon. I guess i have my mind made up (well to be honest there's not alot of choice). It will be paired with a D300.

Can the owners share some experience they have with this lens? or even with the older version is fine. Specifically i'm interested in its weakness. So stuff like how it performs wide open, under extreme lighting conditions, CA level, bokeh, handling, etc.

Thanks.