Been at transport forum (http://www.edinburgh.gov.uk/info/20016/travel_and_parking/658/transport_forum)
One item that will be of interest is that a 20 mph proposal will go to transport cttee soon, and out for consultation after that.
One interesting fact that came up - Tony Kenmuir of central taxis said that they had conducted an experiement with 30 taxis, leaving their offices on Gilmore place, and taking a set route up the mound, around through morningside, at different times of day. 15 had to drive at no more than 20mph and 15 had to drive at 30 mph whenever they could.
They found no difference in duration of journey. And reduced fuel consumption when at 20mph.
Another commonly raised concern (debated here previously) is particulates/pollution. Phil noble from the council says that evidence of higher particulate tends to be studies where they're just studying engines going constantly. But studies from London, where they tested roads with controls (ie similar roads at 20 and at 30) and actual operating cars, showed a very small diminution of particulates at 20mph, and possibly small increase of carbon monoxide. But generally little to no difference.