I lost the original thread about this... It said that Aberforth, Dumbledore's brother, is the bartender at the Hog's Head.
Clues:
Aberforth was in trouble for "inappropriate charms on a sheep" and the Hogs Head smells like sheep. (may have been a goat, I'm tired and don't want to look). Also, Harry felt like he very vaguely recognised the barkeep at the Hog's Head.
Anyway, in HBP, (don't worry this isn't really a spoiler), when Dumbledore recalls a past conversation with Tom Riddle/Voldemort, he says that he's "on friendly terms" with the barkeep there. (once again, I may not have the quote there just right, I'm just tired and don't want to bother myself with looking it up.)
Didn't Rowling say something in an interview in July about the importance of Dumbledore's family in the seventh book?