I think a lot of people still do underrate Maria. They see the teenage blonde and say "Yeah. She had a lucky win, and everyone wants to make her the next kournikova."
But winning a slam takes a lot more than luck. And if you examine Maria's game and her attitude to playing tennis, you will find a game that contains enough high quality attributes to frighten a lot of the top players. People pull out losses she had when she was fifteen or sixteen and say "Oh. She lost x 6-3 6-0" or something, but such scores are virtually meaningless when someone has developed their game at the rate she has.
Official Hitman of the Maria Mafia