Personally I'd try making the account name .. less visible, but I also want to limit the number of changes I make to the forum software (there are already plenty @.@). Not knowing someone's account name gives an added level of security, because to get in, not only do they need to guess your password, but your username as well.
So - it's a nice catch. However I'd be more inclined disabling the private message system, and integrating in-game mail in a separate feature.