If preupgrade had a special user agent string assigned, we could find out how often people are using it to do an actual preupgrade. Currently we can only tell how often it goes to find releases.txt, which may or may not be followed by an actual preupgrade process.
implemented here: https://fedorahosted.org/preupgrade/changeset?new=dev%40dev%2C294&old=dev%40dev%2C293 tested as well. I'll make a new update for f10/f11/rawhide "soon"