[Reasen]

Esta es mi manera favorita

Código Delphi [-]
function GetPCUser(): string;
var
  User: array[0..255] of Char;
  SizeOfUser: Cardinal;
begin
  FillChar(user, SizeOf(user), #0);
  SizeOfUser := SizeOf(User);
  if GetUserName(User, SizeOfUser) = True then
    Result := string(User)
  else
    Result := 'Unknown';
end;