La macro funciona cuando se tiene sólo 2 valores a más como mínimo, y No cuando se tiene un solo valor.

Sub Duplica()
Application.ScreenUpdating = False
Dim REPETIR As Integer
REPETIR = Range("O3")
Range("B8").Select
Range(Selection, Selection.End(xlDown)).Select
Selection.Copy
For Q = 1 To REPETIR
Range("B50007").End(xlUp).Offset(1, 0).Select
ActiveSheet.Paste
Next Q
Application.CutCopyMode = False
Range("B8").Select
Range("G8").Select
Range(Selection, Selection.End(xlDown)).Select
Selection.Copy
For Q = 1 To REPETIR
Range("G50007").End(xlUp).Offset(1, 0).Select
ActiveSheet.Paste
Next Q
Application.CutCopyMode = False
Range("G8").Select
Range("A8").Activate
Application.ScreenUpdating = True
Application.ScreenUpdating = False
Application.ScreenUpdating = True
Application.StatusBar = "Ejecución terminada."
End Sub