I'm continually fascinated by the process of book cover designs and redesigns. I actually follow several blogs that focus on nothing but the subject of new book cover designs, often comparing hardback to paperback and US to UK or international versions. It's really interesting how books are sold in completely different ways in different countries. Re-released versions are also alternately fascinating and disappointing, depending on the thinking behind the updated version. Here's a good example:
On the left is an earlier cover for The Diamond Age by Neal Stephenson. The cover on the right is for a version re-released this year to coincide with Stephenson's upcoming book, Anathem. For some reason all of Stephenson's books (except for the Baroque Cycle) are being re-released with covers that match the style of Anathem: a shadowy figure, lit from behind and walking or running through a doorway at the end of a long hall or large space.
It's kind of bizarre, especially since the new cover makes The Diamond Age look more like a Jason Bourne book than a post-cyberpunk / steampunk / fantasy novel about a girl and the virtual world that exists in her diary. The old cover may be a bit dated and "of its time", but I think it does a much better job of communicating what the book is actually about, with its juxtaposition of rusty gears and amorphous 3D imagery.
If you're interested in checking out a few good blogs focusing on book cover designs, here's my reading list: