For me, the focus is going to be on Arduino projects, but that does not preclude you from bringing whatever you are working on.
Just show up!
I have also set up a google group for announcements of other similar upcoming events only:
Here are the details:
Saturday May 30th 2:00PM - 5:00PM
911 Media Arts Center
402 9th Ave N.
Seattle, WA 98109
The event is FREE but I am suggesting a minimum donation of $5.00 to help 911 and defray their costs a little.
If you have questions email me at openhackday [at] gmail