aristotle - 12:51 pm on Nov 15, 2012 (gmt 0)
Everyone should keep in mind that getting a lot of backlinks removed reduces the amount of "pagerank juice" that a site receives. This could explain some of the cases in which rankings have dropped after backlinks were removed.
As for the disavow tool, I think that it's too soon to reach any conclusions about its effects. We'll probably have to wait until the the next Penguin update or refresh to see anything.