Did chrome or Firefox recently change the way they handle nonexistent DNS answers so that opendns '404 pages' would no longer work? If the writing was on the wall it might make sense for opendns to get ahead of it, since there wouldn't be much they could do to combat browser level changes.
Or:
Did google/yahoo not renew their search feed agreement with them to be the search provider and/or significantly change the rates? I know google has been coming down very hard on toolbar makers so perhaps this is googles way of getting out of that biz (And forcing opendns's hand)