There is an intorductory Arduino workshop/hackfest happening at Saturday House (hosted by Giraffe labs). I am not sure of the current status but it is being organized on their google group:http://groups.google.com/group/saturdayhouse
I am teaching a workshoop at 911 Media Arts starting in November:http://www.911media.org/workshops/arduino.pl
I am also interested in meeting up informally with anyone in Seattle who is messing around with Arduinos.