The first time I really noticed that Mary was, well, not very objective, was the US Open qf's in '03 with Agassi vs. Coria. Wow, she made it known that she didn't like Coria and expressed it every time she was allowed to commentate a Coria match.
The biggest problem with Mary is not being objective. She picks favorites and hails them throughout the match until they lose.
But the worst...was last year during the French Open when she kept saying "Uncle Toni!" in this odd voice, and laughed every time she said it like it was just the funniest thing. It was terrible.
I like Cliff, even thoug he always gets the score wrong. He and Mary don't seem to get along, and it's been a while since I've heard them commentating together. I think maybe once recently.