Sony has announced the imminent closure of its Sony Reader Store in the US and Canada. The store will remain in operation until March 20, after which it will cease ebook sales.
On or around March 20, my book listings at Sony will disappear. According to my publisher, you will have ample opportunity to backup your purchases. Kobo will assume control over Sony's customers' libraries, enabling Sony customers to move to Kobo and maintain access to your books.
You can find more info about the closure of Sony's Reader Store here.