I came back from LHR on Sunday. It took about 15 seconds to clear immigration with the GE photo scan and since I had only carry on, was out to the curb in about 3 minutes from the time I went down the escalator to the immigration hall. The walk from Gate 159 to the escalator to immigration hall was much longer

The photo scan was quick but the screen flashed a message saying "proceed to officer" which just means exit in the direction of the CPB agents sitting at the end of the GE kiosk area. But most people assume means they had to get release by the CPB agents sitting there so people just queued up in front of the desk instead of walking out and a big line started to form. The officers had to keep telling people to just go and not stop. They probably should change the wording on the screen to "proceed to exit".

Edit: I guess "proceed to officer" may be intentionally ambiguous so the CPB agents can still stop you and perform secondary screening if they see you are acting funny?