I think they all have some work to do on their serves.
Nadal showed some
improvement in that dept. during AO 2012, with increased variety and willingness (and ability)to go up the 'T' in the ad court. Overall, I thought there was an obvious change in strategy (especially against Nole) on the serve to be a bit more aggressive. If he stays the course and continues to develop this aspect of his game, Raf may soon possess the key to break the spell DJoker has cast over him in recent months.
Perhaps this will be the next evolution in men's tennis.
Players develop serves and returns that can be used as powerful weapons to set up points for their almighty groundies.
I am eternally astounded no female player has sought to excel at these most important aspects of the game in order to dominate the lackluster field of the past millenium. JFC, how hard is it?