Ken Silverstein gives some pointers on what to look for tonight:
If Obama wins North Carolina, expect him to romp to a huge victory as that would suggest that a number of closely contested red states go Democratic.
An Obama victory in Florida or Virginia would also be fatal to McCain. Victory in both augurs a landslide. If he loses both, it would suggest that the electoral map is reverting to form and we might be in for a long night.
John McCain can’t win unless he takes Pennsylvania, which should be a key early indicator. Because if Obama loses Pennsylvania, it’s hard to see him winning in places like North Carolina or Virginia anyway.
I'll be watching for McConnell in Kentucky. If he's safe early, we are in a normal election swing. If he goes down, all bets are off.