Admittedly this is the first time that I have transited Seatac but I found the process very onerous. Arriving on a Lufthansa flight from Europe and connecting with an AC flight to Vancouver - a process that took 3 hours! Immigration Control was slow and as Canadian citizens we were not advised that we could use the Areas 5 and 6 reserved for US citizens until we were well into the lineup. Once dealt with by a very pleasant officer we had to go thru TSA inspection which took a while by more pleasant officers (did u know that there were regulation sized plastic bags for your liquids??? I sure didn't!) and then had to take 3 count 'em three trains to get to the North Satellite where our Jazz aircraft departed from! And we only made it because of a helpful United Airlines employee - certainly not because of any useful signage! We probably wouldn't choose to travel via SEA again if we could help it it was far too stressful.