From the ABA:
Here's the plan: We book nerds [authors] will become booksellers. We will make recommendations. We will practice nepotism and urge readers to buy multiple copies of our friends' books. Maybe you'll sign and sell books of your own in the process. I think the collective results could be mind-boggling (maybe even world-changing).
Which is, of course, totally fine.
For me, as a reader, I like the idea, as it'd be cool to interact with authors in a more personal way than the Please, Sir, Will You Autograph My Book For Me. And as a former bookseller, I like the idea because, again, it's a more creative program idea than the usual booksigning.
I kind of think that it comes down to how you define the event, I guess. Alexie calls it "volunteering"; Halpin calls it "working for free". But really, it's just an author appearance in a different, more casual format: I sincerely doubt that the booksellers would have the authors schlepping boxes of books around or alphabetizing or shelfreading or, I dunno, cleaning the bathroom.