Magnus Norman is the answer for me.
Rafa´s upset just rushed the process imo.
I think this is pretty much it in a nutshell. In my opinion the single biggest change from the pre-2009 Soderling to the current one is the mental side - such that he has to some extent been able to change many spectators' perceptions that were previously against him. Of course it is easy to overstate Magnus Norman's role in his newfound mental fortitude, but surely the two are more than just a coincidence. Also as duong mentioned, Jenni may have also been a strong influence.
Not meaning to be deriding in any way here but in a predominantly baseline era his height, strong serve and powerful, flat forehand were always indicative of potential success. I think adopting an improved mental approach to his game enabled him to pull improve his results, which in turn fed back to increase his confidence and most probably his desire to practice and improve.
As far as the Nadal match at the French Open is concerned, I agree with Aaric that it just made the above process happen a lot quicker than anyone could foresee. But the way he has been able to self-perpetuate this cycle and achieve very consistent results over the past year has definitely exceeded my expectations. I hope he can sustain it for the rest of the season to qualify comfortably for the World Tour Finals.
And to address GugaF1's point, his technique is indeed probably the most 'ugly' amongst the top professionals but in some way that is a moot point. I don't particularly like Del Potro or Gonzalez's backswing on their forehands, but that doesn't stop them from being amongst the most effective shots in the game. For good or for ill, his style of play seems to work against most players these days and to his strength he is able to transfer his game well across the surfaces so that he remains in contention throughout the whole of the season.