Slightly off topic, but I am actually surprised "vim" was not a taken user name. Does GitHub grant special projects like vim its name if the name is taken but inactive?
I believe you can email github and ask for a certain user name and they'll give it to you if it has no or very little activity. For instance, Ken Thompson joined github a little while ago and he got the user name 'ken'. Don't know how he did that, but I guess it helps being Ken Thompson.