The actual halfway point of the AT is in Pennsylvania, at Pine Grove Furnace State Park. Apparently, tradition demands that thru-hikers eat a half-gallon of ice cream to mark reaching the halfway point.
I'm not sure about the details - how the ice cream is supplied, what the flavor options might be, etc - but I'm pretty sure I'll be up to the challenge if I make it that far!
There is a new Appalachian Trail Museum at the park that opened in 2010. If you visit their site, you can nominate your favorite hiker to be considered for their Hall of Fame!