Avoiding the use of pseudonyms online is not just good advice for public figures, it works for everyone. The freedom of the Internet doesn't mean you can do whatever you want without consequence. Many ways exist to trace "anonymous" posts. The Los Angeles Times, for example, used Internet addresses to trace Hiltzik's postings back to his work computer.
When speaking about the Internet at conferences or seminars, I give this advice about e-mail, posting comments in a forum, or sending instant messages: Don't write anything online that you would not like to see on the front page of The New York Times. Ask Bill Gates: That's where his e-mails ended up during the Microsoft antitrust case in the late 1990s.
On the Internet nobody may know you're a dog. But don't count on the fact that someone won't be able to find out where that dog lives.