I am a number, I am a free man!

Email from Rich at Dribbble:

Hi Peter,

I'm writing to let you know that I changed your username at Dribbble from 555... Yours was the only all-numeric username and unfortunately causes a bit of ambiguity in our system - players can be looked up by username or system id, so if a username is numeric, it prevents access to the user with that id. (This is especially problematic for clients of the API.)

I apologize for the inconvenience of the switch.