Cannot wait for this match !! Personally, there are a lot of unsolved questions about Federer, Nadal, professional tennis's direction in general, that this match will give us, the viewers, an inkling of knowledge about.
Things to watch out for (just my opinion):
1. Nadal's first serve percentage - will it be dreadful like it was against Nole (29% in the second set!) in the final @ IW last week? If so, serious trouble.
2. How many times Federer approaches the net. Will he approach the net during a baseline rally to Nadal's backhand, and approach to Nadal's forehand when attempting to do S&V? Roddick played this tactic very successfully at WTF in 2010.
3. Federer's backhand at the WTF in 2010 against Nadal was brilliant - the main tactical feature of that match was just how often Federer ripped his backhand against Nadal, cross-court especially, will he here as well?
No doubt about it, Federer is a better hard-court player than Nadal, if he is on his game tonight, keeps his concentration up (not like being 5-2 up in a set and losing it 7-5 aka Djokovic match @ AO) and cuts out any errors from his forehand, Nadal is going to have to be at his very, very best to compete.