I found that travel books usually just don't look great on e-readers. The need to go back and forth frequently, to see maps in detail, etc. Zoom, bookmarks, highlighting, screen resolution just aren't up to the task of quick browsing.
So I usually print an e-book before I go somewhere. Usually 2 or 4 pages per page on both sides. As much as I hate doing this, I found this is the way to go until e-readers improve.

Reading regular books is totally different process for me, and e-readers keep up fine.