aurora ave is not bad once you hit the snohomish county line and the 3 lanes of traffic become two lanes plus outside lane bus, bike and right turn traffic only.
riding the viaduct is illegal; also the west seattle high bridge and portions of I-5, I-90 and 520. everything else is fair game in the greater seattle area, i believe.
Here's some video i shot riding critical mass on the viaduct:
http://www.youtube.com/watch?v=vSW_fDS4_sQ