Warum klappt das Label nicht

[Luckie]

Delphi-Quellcode:

type
  TForm1 = class(TForm)
    Label1: TLabel;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function UserName: String;
var 
  Size: DWORD;
begin
  Size := MAX_COMPUTERNAME_LENGTH + 1;
  SetLength(Result, Size);
  if GetUserName(PChar(Result), Size) then
    SetLength(Result, Size)
  else
    Result := '';
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Label1.Caption := UserName;
end;

Ein paar Grundlagentutorials / -bücher wären wohl nicht schlecht.