Not really. Most people use the same username or a slight variation thereof for everything they do online. If I read a LiveJournal post you write, I can probably Google your username and discover 90% of your contributions to the web instantly. From all that data I can probably learn enough about you to be scary (where you live, who you hang out with, hobbies, past relationships...), and Google itself could learn basically anything.
Of course all of this varies person to person, but it's already known to be an effective heuristic by the password-stealing community. Point being: we live in a time of powerful data mining algorithms, and they're only going to get better. Anonymity does not come easy.
Sure (i just googled my favourite username, and found indeed some pretty old stuff that i'd rather keep forgotten). But listing all the appearances of your online persona is one thing, being able to search for your real-life name and retrieve all the embarrassing info attached to it is another. I'm not saying privacy-conscious persons should obfuscate absolutely everything they publish, but considering how things work, the least anyone should do is to make the retrieval of such information a bit more difficult.
Of course all of this varies person to person, but it's already known to be an effective heuristic by the password-stealing community. Point being: we live in a time of powerful data mining algorithms, and they're only going to get better. Anonymity does not come easy.