I bought Rick Atkinson's "The Day of Battle" for Kindle (a history of the invasion of sicily and Italy in WWII); the biggest issue I had with the books was the maps. They were legible, and were better when zoomed - but still weren't as good as maps in a paper books would have been.
The map flaw was ameliorated by the fact that the author put interactive maps on his website, and these maps were better than the maps in the paper book.
But in general, I think that history books are going to be hampered by e-books' general inability to display maps and pictures very well.
Having said that, if certain display issues are worked out, the ability to offer an ebook with simple interactive maps would be a plus (and I am generally skeptical of "enhanced" ebooks). Here's a link to one of the interactive maps:
http://www.liberationtrilogy.com/day_of_battle_map.htm