mac address is just how the system differentiates your device from other users. it holds no personal info. IP address is like a phone number for your PC, and is easier to track, but again, holds no personal info.
also, people offering free WiFi really can't FORCE you to not view something.
it is POSSIBLE to track someone down from information gathered, but it is EXTREMELY hard to do. so much so that most people don't want to put money into doing it, much less tracking what every single user visits. so instead they use "agreement" pages, and let peoples' fear and guilt keep them from visiting such sites, since they don't have the wherewithall to do anything more.