The San Fransisco culture (home of the wierdos...:^)...) does have cable cars and street cars as an icon as you say - but I don't think that they have ever had any that are double deckers.
The cable cars are different than the street cars, and I don't think the cables could pull a double decker up those hills. The stret cars would be limited by the height of the power lines.
Good info here --
http://www.sfcablecar.com/
According to this history page, there are not any double decker street cars anywhere operational (in regular service) in the world....
http://www.sfmta.com/cms/mfleet/histcars.php
They are a good tourist attraction, and Tucson just expanded it's line downtown...
http://www.railwaypreservation.com/v...ley/tucson.htm
They even "recycled" a 30's trolley from Brussels for the route...
http://www.oldpueblotrolley.org/1511.htm