Note, though, that this deal only covers libraries; Overdrive's retail partners won't be involved. But on the upside the content will be available fairly soon.
This is a smart move on the part of Pottermore; it's going to tide over the obsessive fans until the ebookstore launches. But there's still no word yet on when that will happen. I'm still waiting to hear back from Pottermore on their launch plans; I will update this post with their response.
The Pottermore ebookstore was supposed to launch last October but has been indefinitely delayed. If and when the Pottermore ebookstore opens, it's going to support multiple ebook formats (including Kindle, Epub) and be the only place to buy HP ebooks and audiobooks.