We were in Bar Harbor this past weekend, and had a fantastic time. Unfortunately, we didn't get to spend a lot of time in Acadia because of the rain, but we did drive to the top of Cadillac Mountain for an amazing view. I second the recommendation of Geddy's for lunch. Good food, great atmosphere, and reasonable prices. We also liked Stewman's Lobster Pound for dinner, and their little ice cream place next door was great. Also, if you get a chance try the Two Cats Inn on Cottage Street for a great breakfast.
We didn't get a chance to try the Dive In Theater, but the innkeeper where we were staying told us about it and said that everyone raves about it.
Enjoy your trip!