Libby had a great post a couple of weeks ago, What Makes you Pull a Book of the Shelf? which was very apropos for me. I'm knee deep in a new novel but I can't think of a good title. That annoys me and I find myself easily sidetracked, unable to concentrate on the "meat" of my writing because I can't think of a wrapping.
Because for me, my best books usually have titles that come easily-- like The Year of the Dog. They match perfectly and come to me effortlessly. Other books, however, are named by default-- in the end given titles that are just simply adequate because I couldn't think of anything better; and those books have somehow always fallen flat. In general, title difficulty = bookselling difficulty.
So, with this experience in mind, I am a bit worried about my new book. I'm trying really hard not to let it have a "default" title-- I'm so desperate that I've taken to testing all the candidates at the titlescorer. I haven't yet hit one that has more than a 41.4% chance of being a bestseller. I think I'm going to need better odds than that.