I've just been testing the Flickr mashup tool & actively requested only CC licenced images; though at least the first screen got were all rights reserved. Also, for the search term I'd selected, (pretty generic!) - whichever option I picked (i.e. All, CC, CC to modify etc., etc) I got the same number of results - where as on Flickr's site itself, for "any licence" I got the same number of hits - but selecting CC there dropped it to about 10% of the previous total (as I'd have expected)
I wasn't logged into Flickr at the time of searching, in case that makes a difference.