You're right in that you don't see women umpiring men's matches that often. You also don't see ATP members encouraged to do seductive--and in some cases, distasteful--advertising in order to sell the tour (but I had to laugh when I saw the new Roddick Lacoste commercial).
Then there are the people on this board who say that sexism benefits women. They would never say that racism benefits people of color.
But I find that most of the sexism comes from the sports commentators. I wish Kim had slapped Enberg when he said "Can I hold you?" after she asked to hold the microphone at the U.S. Open. Then there's Brad Gilbert, hoping for a "cat fight" between two of the women. And Pam Shriver--when Jon Leach was referred to as Rick Leach's brother--saying "He would hate it a lot more if he were referred to as Mr. Davenport," as if that would be such a terrible thing (she wouldn't be offended if Lindsay were called "Mrs. Leach").
Or how about Brad Gilbert at the French Open, saying that "the lady umpire is coming down to check"? Or Sports Illustrated calling Clijsters "the sportsman"? Or all the bashing of Kim as no longer a "nice girl" once she won the U.S. Open? Or Ted Robinson's reference to the members of the tour as "young ladies"?
Or how about Al Trautwig lying down on the ground next Sharapova while she read a book? Or Jim Courier being all shocked and calling Bovina "aggressive" because she pumped her fiist? Or his saying that meltdowns occur only in the women's game?