Let's not forget Maine isn't the only state that does that. Nebraska does, too. And Nebraska 2nd encompasses Omaha and the surrounding area. What support Obama has will be centered there, and a big turnout could flip that.
Neither NE nor ME will split its EVs in 2008, but McCain’s fight for the ME-02 (47% for Gore in 2000, 52% for Kerry in 2004) is less pie-in-the-sky than Obama’s campaign for the NE-02 (which gave President Bush 57% in 2000 and 60% in 2004).