Its quite annoying if someone else visited you and used your skype to login on his/her account. That account appears all the time the next time you start skype. If you whish to remove remembered skype username from login screen than open up explorer and navigate to:
C:/Users/YourWindowsUsername/AppData/Roaming/Skype
Change slash to backslash in code above!
Remove folders that contains username(s)
Restart skype!