CAMBER BAR SQUATS

This is probably the oddest looking bar and like the Buffalo Bar, great for relieving stress off of the shoulders. But the bar is much more than shoulder relief – it really turns squatting into a different movement.
What most people first notice when using the Cambered Squat Bar is how unstable the bar is. The weight rocks back and forth and forces the lifter to stay very tight and controlled. While this might sound like a good thing, this makes it the last bar I'd let a beginner use. When someone is trying to learn a new movement, the last thing you want to do is throw more curveballs at them.
The concentric phase of a squat with a Cambered Squat Bar is always interesting. Due to the instability of the bar you can't push as fast at the bottom, but you have to push tight; tighter than you normally would (or should) with a straight bar.
This is a great way to remind you to stay tight and push with a controlled and steady force out of the bottom of the hole. For someone that spent their life training with a fast concentric phase, this was a real learning process for me. But slowing down with this bar allowed me to learn how to squat faster because the concentric phase had to very focused.

EXCERPT FROM:by Jim Wendler
http://www.t-nation.com/free_online_article/most_recent/6_specialty_bars_for_strength_and_size&cr=