Actually, on an open wi-fi network, it is not only possible but tremendously easy to strip SSL away from any info. A friend of mine, a software engineer, was actually on a CBC segment a few years ago demonstrating this--at a public library, they had the reporter use the open wi-fi, and login (with fake data) to very-well-encrypted online banking; 10 seconds later they had her login information in text form on their laptops.
It is a common misconception that, when on unsecured wi-fi, SSL still works. It absolutely does not. Anybody standing in that subway station can, with near-zero effort, get your twitter username and password--though twitter login or not, yes, anything you enter while connected to the network has always been subject to that risk as well, I solve that by simply checking traffic and streetcar positions on the wi-fi, which I can no longer do without exposing my twitter password at these new stations.