To be fair legally binding or not, proving that you were the person that signed up (especially online) is tenuous at best. Most people have multiple users on a single IP address and the "I never signed up to it it must have been my housemate, mum, dad, brother, sister, Some bloke using my wireless) would be an easy get out clause...
THAT SAID.... I seriously doubt there will be that many people dropping out and as some have suggested I would imagine that the number of extra people jumping on board will more than accomodate for them..
Personally can't wait to pickup my membership, even with working various weekend hours and Friday nights it's going to be more than worth it