Paul Karlsgodt over at has an outstanding post up that outlines his thinking on when (and how) a defendant should challenge the certifiability of a class.  He explicitly recognizes that 

[T]here is also an art to defending class actions, and part of the art is in knowing whether to challenge class certification at each available opportunity. Of course, because this is about the art and not the science, there is no single answer to this question, but below I have tried to sketch out some of the possible considerations in making the decision to use various different procedural devices at different phases of the litigation.

(Emphasis in orginal.)  The general advice that follows is a very helpful summary of the different opportunities to challenge the certification of a class.  

I’d quibble with only two aspects of his post: (1) Paul and I have slightly differing opinions on the usefulness of the motion to strike class allegations.  (2)  I would really have liked to see his take on whether to file a motion to deny certification (a rare, but increasingly useful strategic option).  

But these are quibbles.  What Paul has done here is what co-author Brian Anderson and I were aiming at with The Class Action Playbook: he’s given an excellent summary of each opportunity to challenge a class, and set out his views of the risks and benefits to each challenge.  

Go, read it for yourself.  I assure you, it’s time well-spent.  

[Dislcosure: Paul gave this blog an early boost, and provided a very nice review of the Playbook.]