In the downtown area, I would see about that ratio in passenger helicopters, rather then t-birds themselves. I would see t-birds in the built up area to be much rarer (and perhaps more likely to attract attention).
Also, many of the larger buildings have security systems designed to warn and then attack aircraft which approach to close. I would recommend any flyers in the metro area have a map of the skylanes or risk running into 'issues'.
Outside of downtown, it would depend on the area, but I would imagine most people would be use to aircraft flying overhead at all times. Corporate headquarters liek Ares in Bellevue or the Aztecnology Research Park in Tacoma would see helicopters and possibly t-birds even leaving and arriving at all times of the day, while an aircraft in the Barrens may be a chance to trigger a 'blackhawk down' style situation. That said, smuggler t-birds skim in and out of the lava fields in Redmond all the time. Fort Lewis would see only military approved aircraft.
