The TPL is reportedly the only library in Canada that has an affiliate deal with booksellers (I'm not so sure that is true), and in the past 5 months they have sold 509 books. But the idea isn't all that new.
Both OverDrive and Bilbary offer similar programs. Bilbary's partners include Califa, the Kansas State Library, Douglas County Libraries (CO), and other library systems, while OverDrive enables any of their library partners to also direct patrons to any of several hundred ebookstores. When I last checked (around this time last year) OverDrive's program was available around the world, not just in the US. I was told that OverDrive had 300+ retail partners, including the major US ebookstores as well as a group so diverse that it even include Nokia.
Curiously enough, the TPL does offer ebooks via OverDrive. I wonder why they didn't use OverDrive's service instead of signing a deal with Kobo?