Taken at face value, Dropbox's indicator is particularly interesting:<p>> ChenLi Wang, who runs the growth team at Facebook [sic: Dropbox?], said that the leading indicator of an engaged Dropbox user is when they put at least one file in one Dropbox folder on one device.<p>Basically - the leading indicator is any use at all. The other business' all had, relatively, a much higher threshold.<p>This is probably because Dropbox is immediately useful and stupid-easy to use.<p>Of course, it's hard to take this at face value since we don't know how everyone is defining an engaged user (and each definition isn't directly comparable to the other services' definitions).