We say and do things on the web that we would never do in person.

That has never been the case with me. As a matter of fact, I'm more cautious online because I am creating a permanent, public record. I may feel this way because I'm from an earlier generation. I love to engage online, but I'm always aware that when I write something, it's there forever. I wouldn't want a lot of my casual conversations to be there forever :)