I just bought one from Amazon during the one day sale at $762 next-day shipped... and it's going back. It's fast on my D200 but not "MAN that's fast" which is what I was hoping for. IQ was nice, a bit of AF hunting in low light, 2.8 is a bit soft at the extremes. For the money it would be my choice hands-down but I think I am going to pick up a 70-200VR instead. Good luck to you!
I have the newest version and am very happy with it. I guess I must be less of a pixel peeper because I fell my images shot wide open look fine. It is minimally softer at f/2.8, but you have to view the image at 100% crop to notice it. It is at it's sharpest from f/4 to f/11. I have used it on both a D300 and D70s with great results. The 1.4x tc works great with it with no drop off in image quality.
I find the AF very fast, enough to use shooting sports with no problems. I had an old screw drive Tokina 80-200/2.8 that took forever to AF compared to the Sigma.
The Nikon 70-200VR is a better lens wide open, but for almost a grand more you would expect it to be. If you don't need VR, I find the Sigma a nice alternative.
I'll add to my comment above by saying that I also have an 80-200 AF-D two-ring and like that better than the Sigma as well. Far better overall feel to the shots and I thought it was faster. Might be a good find at KEH.