Damn ha, that's a very positive reaction by the Dortmund fans. Really thought he would have gotten some serious stick by them for going Bayern.
I think it's got to do with the fact that while the proposed move was behind BVB's back, when he realized that BVB were unwilling to sell him when he wanted to go, which was last summer, he didn't morph into a petty diva like Tevez and instead got his head down and gave the club and fans a solid season.