Danke Anke, the difference between Hingis/S.Williams and Graf/Navratilova is that the former have reputations of being *brats*, whereas the latter do not. Dominant number one players on the WTA tour rarely receive more cheering than their opponents; and in Serena's case she has been the most dominant player since Graf, circa the late 80s. But when you're this dominant -and- a player who has a tendency to be bratty at times, crowds are going to be even more against you. I'd bet you a million bucks that if Chanda Rubin ever became a dominate number one player that she would NEVER receive the kind of treatment that Serena did today. Why? Because she's classy and has always been classy. She doesn't have a history of defaulting matches; she doesn't have a reputation for brushing off everyone in the lockerroom who isn't her sister or Alexandra Stevenson. She doesn't have a history of suddenly having mysterious injuries when she's losing matches in Grand Slams; and she doesn't have a history of rarely giving her opponents any credit. And so on, and so on.
In short: there are some major differences between Serena Williams and other former number one players. Just because Graf was never booed to the extent that Serena was today that doesn't mean you can attribute it to race. That's just sloppy thinking. The fact of the matter is that Serena has a personality which many find disagreeable and annoying (including myself). She may be able to kick her older sister's butt on a tennis court, but she has a heck of a lot to learn from Venus and other former number ones when it comes to handling herself, both on and off the court. Although she has improved in this area over the last year (the same way Hingis improved in the years following the 1999 French Open), I still think she has a way to go yet.
[And one final thing: when it comes to Serena Williams and racism, I'd say that there are more people who like Serena -because of- her race than people who dislike her -because of- her race. If you transplanted all her character traits into a white tennis player, she'd probably be as disliked as Irina Spirlea, Natalie Tauziat, or Hingis (in her earlier years).]