Well, if you have you're heart set on Acadia make sure you do it in early June. 4 million people come down here and most do it in Jul/Aug time frame and they all have to pass over a small two lane bridge to get to the island. At times, last summer, we had traffic jams backed up from the bridge almost to Bangor - that's almost 50 miles! Sometimes they were dead stopped for hours.
Personally, there are some beautiful places in rural Maine to see and you don't have to put up with the Coney Island atmosphere. Let me know if you're interested and I'll go into detail.
Went to bar harbor and acadia last year, late June...great ride. Must have been lucky like Crossbowme says - didnt have much traffic at that time of year. Highlight was when in Acadia, rode to the top and started down the mountain and got passed by a bicycle flying down the road. I was doing 45, he had to be doing 10 more than us. Dont know how he made it around those switchbacks. When I got to the bottom and couldnt find him I asked some other guys on bikes and found out he was part of a group of crazy bastards who did this on a regular basis.
I'm looking forward to Bar Harbor but will have to postpone for while. Going to the outwest rally in Aug and now another trip (Milwaukee) in July so Acadia will have to wait just a bit.