When I posted as guest, I could use the exclamation point ! in my username "N! Xau".
I registered as member and once I tried to enter ! I got a warning saying something like "you can't use that character in the username, but you may change the displayed name after".
So i set both username and displayed name as "Nxau", but now it doesn't let me add that little ! in the middle...
thanks
N! Xau