Route 1 is slow going as it's mostly two lanes. There can be a real bottleneck at Wiscasset. Look at MapQuest's estimates of times. They tend to be accurate.
That being said, it's a pretty drive. You can take I-95 to Brunswick or Topsham and then pick up 1. That takes you through gorgeous towns (Bath, Wiscasset, Damariscotta, Camden, etc.). You can cut a little bit off the route by bypassing Thomaston and Rockland; cut across Route 90 at Warren and pick up Route 1 again in Rockport.
If you want to get to Southwest Harbor is less time, you have two optioins:
1. Go I-95 to Bangor, and then take Route 1A down to Mount Desert Island.
2. Take I-95 to Augusta, cut across to Route 3, pick up Route 1 in Belfast.