I'll be following this chart tonight.
This bears notice:
Odds are that rural areas will report their results before the cities, which means that the early numbers should favor Clinton (this may actually be a nontrivial advantage to her in terms of media narrative; the race could very easily be called for her when the ticker shows Clinton ahead by 14, but things could close to within 8 points once all votes were counted).
Update: The Politico says that in Pennsylvania, the cities and suburbs report first. If accurate, that is different than the rest of the country. There are more votes to count in cities, hence the later reporting.
In Ohio, Cuyahoga reported last. In Missouri, St. Louis reported last (hence the blown "Hillary wins" headlines). And so on.
Kitty in the comments says that in 2004, Pennsylvania cities reported first, but in 2006, it was the rural precincts that led the way. I don't know which is which. But if the cities report first, expect big Obama leads that will whittle away through the night.