So terribly sorry that I wasn't here when you demanded your responses... I kinda have a business and a family that tend to demand my time...
What do you want to shoot with it? It's the non-OS version is a macro lens so it's a bit slow on the focus. Not that it's as slow as mud, but if you want it for sports or something you need lighting fast focus for then I'd go up to the OS version. I have the 70-200 f/2.8 OS by Sigma and it's my primary lens for everything. I chose to go with the OS version because of the extremly fast focus on it-I shoot sports.
I also have the Tamron 70-200 f/2.8 and while it's SLOW on the focus it's beautifully sharp for the price and the macro capability is great. It's slower than the Sigma non OS version.
I shoot with a girl who uses the non OS version Sigma and loves it. Her images are beautiful. She does dabble a little bit in sports. She says she misses focus once in a while because of it, but she's not going for professional sports photography so it servers here more than well.