April 23/24 was the date several of my already Pandalized sites were hit again. These were the ones I hadn't developed or adjusted in most cases except by the addition of noindex, nofollow to thin pages.
One site I had developed with longer pages didn't get hit this time.
Another site that was high in rankings got demoted one place by a very long page. (It ends with 200 Comments, lol!)
It seems like a turn of the Panda dial to kick the anorexics and promote the obese.
It is also possible that noindex, nofollow doesn't necessarily help your site any more - i.e., if you have too few quality pages.
Size of pages and size of site could be important factors (more important than previously).