As a Serena Williams fan, I will say that comparing her with Federer is a bit strong. While she might end up winning more slams than Federer, there are quite a number of achievements Roger has, that she is certain not to reach. With that said, I think with a couple more slams, Serena, for me, would be the greatest female player of all time.
Before I leave, I wanna point out that some of these comments are really uncalled for. Whether you do or don't agree with what Sports Illustrated said, you take it up with them, but don't show such nasty disrespect towards Serena, a player that has worked her ass off to get where she is and do what she's done over the course of her career, despite everything she's dealt with. Some of you really need to grow up and move past these silly, childish comments.
To me it seems her ass is only getting bigger. might be muscells though...