If you ever want to change your user name for one reason or another - it takes place immediately and all your old posts now have your new name. This is not so good if you are changing your name for privacy reasons.
It also has your old avatar and siggy.
I thought it would be a brand new account - doh
My advise: go offline for a few days/weeks, change your name and remember to change your siggy and avatar.
I guess I will have to do it again in a few week. Learn from me and save yourself a few bucks.