This article in today's Hill highlights Rahm Emanuel's Hillary-Obama dilemma:
One House leader with potentially divided loyalties is Rahm Emanuel (Ill.). The Democratic Caucus chairman and 2006 electoral hero has close ties to the Chicago political community certain to back Obama as well as to Sen. Clinton and her husband, whom Emanuel served as a campaign strategist and senior White House aide. Emanuel has demurred on the question of his 2008 allegiances, although his brother Ari has helped raise money for Obama.
One thing to keep in mind: Emanuel's loyalties are more to Bill than to Hillary. As this 1998 article from the WaPo notes:
In 1993, Emanuel's brash, punish-your-enemies style aptly reflected a White House in which certitude sometimes outpaced judgment. He lost support internally and, in a move that sources said first lady Hillary Rodham Clinton urged, was fired from his job as political director. [Emphasis added.]
Emanuel strikes me as the kind of guy who has a long memory.