This thing saved my butt last year.
I took a trip to Boston, and drove from Boston to Inverness, Nova Scotia on Cape Breton Island.
I went the scenic route, cutting through Maine to Calais / St Stephen, where I crossed the border into New Brunswick.
I had an atlas, I had maps, I had been studying maps of the entire Eastern seaboard for months and months. This was a solo journey so I wanted to be prepared. I decided to get the Lonely Planet guide on a whim. I figured I couldn't have too much information!
The thing about the Maritime Provinces that outsiders don't know, is that it's nearly impossible to get any good information on them from the conventional sources (internet, etc). Enter Lonely Planet guides.
The biggest way this book helped me was when I was in Saint John, NB which is where I stayed overnight between Boston and Cape Breton.
First of all, Saint John was surprisingly cute. I wish I would have had more time there. Secondly and more importantly, on the way through to CB, I stayed at a slightly crappy motel just outside of town which while not terrible, was not fantastic and I didn't feel entirely safe (just paranoia I think, but still...) That motel was NOT listed in the book, FYI. So on the way back, I decided to look elsewhere - in my book! Lo and behold, I find in the book the contact info for the summer dorm rental program at the University. Why yes, I'll gladly shell out $20 for a safe, clean room! I just needed a place to sleep after all, and it was perfect.
The book also gave me some great info on tiny little St Stephen, where I had a few minutes to stop before crossing the border, and I hit a chocolate shop recommended in the book. Divine. Wouldn't have had a clue without my guide book.
I'm quite sure my journey would have been entirely different, and less enjoyable without this thing.
Lonely Planet books are priceless. Get one.