Duff....if you are reffering to socal app then you are correct....upon intial contact 'Heavy" is used and when ever you are following a "heavy" app control informs you of that...for what other reason than situational awareness would ATC give you that info if it were not for wake turbulence?????..... not trying to be a smart-arse here mate....but sitting in ATC and sitting in my cockpit behind a 747,any heavy or a 757 is "situational awarness....falling off your chair in the ATC buliding is not the same as being hit by "good" wake!!!