In case you've missed it (and if you live in or around Seattle, I'm not sure how you could have), The Link light rail line from downtown to the airport will open on Saturday. Sound Transit has details on the opening here. The folks over at Seattle Transit Blog have been counting the days to this, and I have to say that Ben and company really seem ready to party as a result of the long-awaited opening.
There will be free rides all weekend. Be prepared for long lines and crowded platforms and trains all weekend. Also, there are no round-trip rides. To give everyone a chance to ride, once you get to one end, you have to get off the train and get back in line. There will also be shuttles running the route if you don't want to wait in line again.
Personally, I think I'll be waiting to take my ride on Link until after the festivities