I think Hacker News' name policy is just about right. Its public enough that we don't have things going on like 4chan, but its not public to the point people are afraid to comment their opinions.
Did I miss something? I can't find any username policy in HN's guidelines.
The policy, then, is completely implicit: you can have any valid username which may or may not reflect your own name.
Oh, and you can't change them after the fact. As far as I know. That would be a nice feature...