Just a heads up for anyone going through SEA. PreCheck is moving from the N checkpoint to the central checkpoint. This hopefully will make everything a bit faster and less crowded.
From Alaska's
PreCheck page:
On October 21, 2012 the Transportation Security Administration (TSA) will move the PreCheck lane from the North checkpoint to the Central checkpoint at the Seattle-Tacoma International Airport. Look for airport signage that will guide you to the Central checkpoint PreCheck lane.