From the Washington Post:
The arrests in Shanghai were part of Hu’s cautious but relentless drive to cement his power as party leader and ensure faithfulness to his vision up and down the hierarchy. That effort, foreign and Chinese specialists said, will reach a high point at the 17th Party Congress in the fall, when Hu and his lieutenants are expected to stack the party’s ruling bodies, the Politburo and its Standing Committee, with Hu loyalists.
“The political aspect here is much more important than the law enforcement aspect,” one Chinese corruption expert said, speaking on condition of anonymity because of the sensitivity of inner-party politics. “The interesting point here is that before, nobody could touch Shanghai, and now you can. Hu wanted to break the Shanghai taboo.” [Full text]