No surprise: Some places allow pets, some don't. I've noted inns that allow pets, but even here I don't recommend showing up with a pet in tow unless you've cleared it over the phone with the innkeeper. Note that many establishments have only one or two rooms (often a cottage or room with exterior entrance) set aside for guests traveling with pets, and they won't be happy to meet Fido if the pet rooms are already occupied. Also, it's increasingly common for a surcharge of $10 or $20 to be charged to pet owners to pay for the extra cleaning.
Some innkeepers will accept pets but don't want the fact mentioned in this guide. Their policy is to have travelers ask them first so that they can explain the ground rules and ascertain that the pet in question isn't a hyperactive terrier with unresolved barking issues. It doesn't hurt to inquire, even if a pet policy isn't mentioned in these pages.
An excellent resource is www.petswelcome.com, which dispenses medical tips, names of animal-friendly lodgings and campgrounds, and lists of kennels and veterinarians. Also check out www.pettravel.com and www.travelpets.com for more information.
Keep in mind that dogs are prohibited on hiking trails and must be leashed at all times on federal lands administered by the National Park Service (this includes Acadia National Park in Maine). Pets are allowed to hike off-leash in the White Mountains National Forest in New Hampshire and the Green Mountain National Forest in Vermont. No pets of any sort are allowed at any time (leashed or unleashed) at Baxter State Park in Maine. Other Maine state parks do allow pets on a leash.
The Peripatetic Pet--Never leave your pet inside a parked car in hot climates with the windows rolled up. It's a good idea never to leave a pet inside a hot car even with the windows rolled down for any length of time.
Make sure your pet is wearing a name tag with the name and phone number of either a contact person who can take the call if your pet is lost while you're away from home or a voice mail system that enables you to easily check remotely for any calls related to a lost pet.