Pros
Yahoo! is full of extremely smart and dedicated employees. It's a big enough company that you are sure to find some area to work in which you are interested. Yahoo! offers good benefits. It has an informal culture. You are generally allowed to do the right thing. If you're an absolute superstar you'll be well compensated.
Cons
A new way of evaluating employees has come along which, in my opinion, greatly detracts from the once collaborative culture. On a quarterly basis all employees are stack-ranked against their colleagues in their respective departments. They are then placed in a "bell curve" where each slot in the bell curve *must* be filled. If you are in the bottom of that curve for three quarters in a row, you're fired. This means that if you work in a high performing group you could wind up toward the bottom of the bell curve even though you do a good job. This creates an incentive not to help coworkers, to avoid hiring superstars, and to generally not wish good things to happen for your colleagues.