Monica Berger and Jill Cirasella have published "Beyond Beall's List: Better Understanding Predatory Publishers" in College & Research Libraries News.
Here's an excerpt:
Although predatory publishers predate OA, their recent explosion was expedited by the emergence and success of fee-charging OA journals. No matter how strong our urge to support and defend OA, librarians cannot deny the profusion of predators in the OA arena; John Bohannon's recent "sting" made abundantly clear (despite methodological flaws) that there are many bad actors. Rather, we should seek to understand their methods, track their evolution, and communicate their characteristics to our patrons.