The announcement seems to have been posted to the Powell's Books website a couple weeks ago, but it only showed up in my search alert today.
The image at right is pretty much the sum of the announcement. There's no info on when or how Powell's will sell Kobo's hardware and content, though it does seem likely that the ereaders will be available in all 6 Powell's stores.
As for the ebooks, I know of at least one other ABA member who is simply acting as an affiliate, not selling ebooks directly. Titcomb's Books is located in Mass, so I likely won't ever be buying anything from them directly, but the contents of their website suggests that they will stay an affiliate and not act directly as Kobo's agent.
Even though today's news could easily have been foreseen, it still marks a milestone for Kobo. Powell's was one of Google's flagship partners when the Google eBookstore was officially announced. By signing on with Kobo they added to the credibility of the Kobo-ABA deal.