Rachelle Gardner has written a very clear post about the challenges posed by electronic formats to reversion of rights clauses in book publishing contracts:
“Reversion of rights” simply refers to the point in time at which the publisher no longer owns the rights to your book. When the rights revert to you, the author, you’re free to sell them again or do whatever you want with your book. In the past this wasn’t as important because it was unlikely that another publisher would want to take on an already-published book. Your main option was to self-publish and you’d likely not be able to make enough money to cover your self-pub costs.
But all that’s changed in the digital age. Now, when the rights revert, you can simply and cheaply format your book for Kindle and all the other e-book formats, and keep it for sale forever, perhaps making a few extra bucks a year. So there’s a strong reason to want to get the rights back as soon as the publisher is no longer making you any money.
Rachelle provides some useful thoughts on how reversion clauses should be worded to address digital formats. Ivan Hoffman also has some more general suggestions on issues to consider when negotiating reversion clauses in book contracts.