Humor columnist Dave Barry once suggested that Maine's state motto should be changed to "Cold, but damp," thereby emphasizing its two primary qualities.
Cute, but it's sort of true. Spring tends to last for just a few blustery days; November features bitter winds alternating with gray sheets of rain; and the interminably long winter brings a mix of blizzards and ice storms.
Ah, but summer. Summer in Maine brings osprey diving for fish off wooded points, gleaming cumulus clouds building over steely blue rounded peaks of western mountains, and the haunting whoop of loons echoing off the dense forest walls bordering the lakes. Summer brings languorous days when the sun rises off the Atlantic well before visitors do; by 8am, it seems like noon. Maine summers offer a measure of tranquillity; a few days in the right spot can rejuvenate even the most jangled nerves.
The trick is finding that right spot. Maine's Route 1 along the coast is mostly an amalgam of convenience stores, tourist boutiques, and restaurants catering to bus tours. The loop road, beach, and most popular mountain peaks in Acadia National Park can get pretty congested in summer. Arriving without a room reservation in high season is a bad idea.
On the other hand, Maine's remote position and size can work to your advantage. The state has an amazing 5,500 miles of coastline, plus 3,000 or so coastal islands. With a little homework, you can find that perfect little cove or island, book a room in advance, and get ready to enjoy coastal Maine's extremely lovely scenery.
Getting to know the locals is fun, too. These were mostly fishermen (as opposed to the farmers who colonized the rest of New England) and other seafaring folk, and today coastal Mainers -- even the transplanted ones -- still exhibit a wry sense of humor and gregariousness. There's a Bait's Motel in Searsport (complete with worm-hanging-off-its-hook motif), and a tiny street called Fitz Hugh Lane in Somesville. Take the time to get to know them.
For more detailed coverage of this coastline, pick up Frommer's Maine Coast, a great resource that will help you fully enjoy this region.