Martina Navratilova, Conchita Martinez, and Steffi Graf's mother used to post occasionally on the AOL tennis board about 10 years ago (in the case of Heidi Graf, even more recently, maybe 8 years ago). And yes, their identities were confirmed.
It was fairly interesting, actually. Then someone hacked the email of either Conchita or Martina, maybe both, and they quit. I think Graf quit because certain posters thought it was a good idea to harass her. MN1956 was Navratilova's name, and I can't remember Martinez's. It might have had to do with a dog or pet of some sort. And Graf's was her grandson's name.