See the details here.
Basically, Syracuse is paying to leave a bit early, as they won't be giving the required 27 month notice. With the additions of Conference USA teams and Temple, Big East was able to lose Syracuse in number. Still, the quality of Syracuse basketball hurts a conference like the Big East.
Edit: Conferences for 2013, with members can be seen here.
This paves the way for Pittsburgh leaving in 2013, as well.