Which services have figured out a way for revenue after gaining users
nostrademons: Google.  That's the one everyone points to.There're a bunch of other ones that look like they're not making any money, but actually are, usually through advertising or corporate deals.  Reddit.  FaceBook.  HotOrNot.  PlentyOfFish.  LiveJournal.  MySpace.  Skype.  YouTube (though I believe YouTubes revenues are less than Google expected when they bought it).