One of the reasons I like reading on a Kindle is that I can look up words I don't know by clicking and holding. It's a way to increase my vocabulary, and decrease my frustration. It's especially useful when reading a book like Game of Thrones where the author uses a lot of old words that aren't used that often.
Here's the idea: Let the book author load up the dictionary with the names of characters and places. Books like GoT that have a huge number of characters, often include a chart at the beginning of the book explaining all the relationships between the characters. Wouldn't it be great if this information were baked into the dictionary as you're reading the book? Of course someday it will be.