he's been completely fearless in big moments ever since he erased the 2 mps against roger at the 2010 uso (an event he nearly bombed out of in the first round down 2 sets to 1 and a point from a double break in the 4th)
ever since those 2 points (even though he lost to nadal 2 days later) it seems as though belief has gone from a major issue/obstacle to a complete non-issue, at least in my opinion. he may not be able to be at the same level as 2011 week in week out, but the belief in big points might be with him for life.
i'd say his 2012 form so far has looked a lot like 09-10, except hes winning more of those matches on bad days (and all of em at majors) instead of folding like he did at majors against kohlschreiber, safin, melzer, berdych, etc.
i really do wish he would stop letting his foot off the gas in 2nd sets though, these past few months there have been a LOT of matches where he comes out and tees off in the first and then starts to go away a bit in the 2nd.