I'm shocked, SHOCKED, that a company that was colluding with competitors to suppress their workers' wages[1] would also collude with publishers to rig the ebook market.
At least in California, I was under the impression that there was really no question--they're totally unenforceable unless you plan to pay your employee full wages for the entire duration that they're not allowed to work for the competition.
But this wasn't about no-compete clauses, this was about the companies having an off-the-books agreement not to give unsolicited job offers to the competitors' employees.
[1] http://www.inquisitr.com/486164/google-intel-and-apple-under...