i've only used GE once, at YYZ, and i got an X. i think the fingerprint scan worked. i was asked to go to a second screening room. there were a few people waiting, but i was seen right away. the officer there looked at the X and asked why i was sent there. i told him i don't know - this was the first time i had used GE.
he asked me a few questions, checked the contents of my bag, complimented how well organized it was (tom bihn brain bag with a brain cell + macbook air, and a hardback book in the one compartment; a packing cube with clothes inside + clear quarter packing cube with toiletries inside in the other compartment), and sent me on my way.