I've downloaded several (free or library) books onto my laptop and my IPod Touch - which is fine for reading, but I don't want to pay to download a travel book (i.e. Rick Steves, Lonely Planet or Frommers) unless I can find what I need for a specific place. So far the ones I have do not have a table on contents or index. If I pay for a guide book, will there be search options or index or anything to help find specific information when I need it (while I do read guide books, it's usually here and there).
I can speak about Rick Steves' Paris and one or two other travel books on the Kindle. RS Paris has a hyperlinked table of contents as well as by-word search capability. The TOC is reached by an option on the menu. Depending on the book it might have an index (RS Paris does not). In addition you can bookmark a particular location.
Having said that, I've found travel books on the Kindle not satisfying and probably won't focus on these much in the future. The images are a little small, you can't zoom in on an image, and it's hard to flip back and forth between a map and the text (on a tour, for example). Any book that you read more or less exclusively in a serial fashion is fine on the Kindle, but I'm not fond of the experience with anything that you read more as a random-access book.