|A signed e-book.|
With e-books, you can still go and hear an author speak, but there's been no way for her to sign your e-book. Some have been in development... and now there's Kindlegraph. It's a way to sign Kindle e-books, and it seems to have some basic issues solved. Basically, you can get an author to write an inscription to you, and the PDF gets sent to you and stuck onto your Kindle book file.
This does mean the author doesn't have to be in physical proximity to you... this can all be done remotely, though of course that's a less compelling attraction than the actual press-the-flesh style book-signing. A more basic problem is that unlike a signed physical book, you have not added any value to your Kindle book... since you can't resell it.
That is one of the key disadvantages of the e-book... it's not lendable or resellable. There are efforts to make books lendable, and I hope someone will figure out the resale part someday. Though that wish is probably not shared by most authors.