To date Sharapova, Ivanovic and Kirilenko. In this order.
I saw a little bit of him last week, and he impressed me as well. He was very committed to his shots, and played well.i saw something from him today that really impresssed me: he was more fearless than ever so that was the first thing that caught my eye. he was aggressive when he knew he had to be.
he served well and returned well pretty much for the entire match. he never let his intensity and focus drop.
he also looks more fit. i think he looks like a man on a bit of a mission this year.