It's not so much the actual username that tips people off. It's the manner in which the posts are worded, usually. Also, opinions don't usually change when someone changes usernames, and the opinions and they way they are set forth in posts often remain the same.Only one username for me.
As a side note, I'm always amazed that people figure out who uses or has used more than one name, by their posts. I don't pay enough attention to usernames to pick up on that.