Bigwebmaster - 12:57 am on Jun 2, 2013 (gmt 0)
I doubt the profile pages are causing this specific penalty as we have thousands and thousands of profile pages as well, except we have had them as noindex,nofollow long before this happened to us on Nov 16, 2012.
Having them as index,follow could trigger another problem though, such as with Panda, but in my opinion this is not the cause for this update. I think your rankings would have dove on one of the Panda updates if it had to do with your "pointless" profile pages, not this one.
It is hard to tell, but I still believe this specific update may be related to user generated content that falls into a category that isn't bad, but not absolutely fantastic either. Content that is useful and isn't thin, but of medium quality like Sgt_Kickaxe first mentioned. That is the only theory that makes sense to me looking at the type of sites that were affected on this specific date.