This story broke today because of a letter sent out by Steve Potash, the head of Overdrive. That letter was only sent out to member libraries, but it fairly quickly started being passed around. Here's the important part:
We have been required to accept and accommodate new terms for eBook lending as established by certain publishers. Next week, OverDrive will communicate a licensing change from a publisher that, while still operating under the one-copy/one-user model, will include a checkout limit for each eBook licensed. Under this publisher's requirement, for every new eBook licensed, the library (and the OverDrive platform) will make the eBook available to one customer at a time until the total number of permitted checkouts is reached.
I have to admire some publishers; they work ceaselessly to make themselves only slightly less repugnant than pirates.