From ReadWriteWeb comes a very thorough-going list of issues to understand as you indulge and participate online. Some good, some not so.
Some of the principal points:
1. Search engines aren't enough. Social sites yield research.
2. Interconnectedness on the Web means sharing information and having it build for others.
3. There is no Delete button on the Web.
4. Standards should remain.
5. Be careful, very careful, about what you post.
6. Be mindful of who's following you online.
I have to admit, the list sounds like a cautionary tale for everyone I know, and me at times. I remain surprised at the casual nature of commentary, at the speed with which people are prepared to pronounce on others' hard work, and the risks people take in participating.