I spent several weeks looking back and forth between the Nikon 24-70 f2.8 and the new Sigma 24-70 f2.8 HSM. Man, was it a toss up. On one hand, I wanted to stay with as much Nikon gear as possible. On the other hand, I'm a cheap bastard at times and was looking to maximize the amount of stuff I could get with the budget I had. $1800 for the Nikon lens wasn't going to cut it, no matter how much I lusted after the lens.
I'm entirely pleased with my choice.
The one downside is that the lens is huge. heavy. beastly. It's like the eye of cyclops staring you down and peering into your head while you scream for an escape.
I love the bokeh on this lens too. I haven't yet been able to do a full out shoot with it, but I've certainly played with it taking photos of random stuff (like squirrels).
In other toybag bits, I also got the new Nikon SB-900 and more portable light kit for it. That brings my overall light kit to three flashes so I can do more stuff outside of the studio.
Anyway, it's two more bits of stuff for my kit. Yay!