I’m sure this is simply a coincidence, but the Center for Responsive Politics has discovered that the candidate who gets their support tends to be the one who gave them the most money:
For those elected officials who had endorsed a candidate as of Feb. 25, the presidential candidate who gave more money to the superdelegate received the endorsement 82 percent of the time. In cases where Obama had made a contribution since 2005 but Clinton had given the superdelegate nothing, Obama got the superdelegate’s support 85 percent of the time. And Clinton got the support of 75 percent of superdelegates who got money from her but not from Obama.
Here’s an up-to-date chart of which superdelegate got what and from whom.