mikerickson,
Your code is working as desired, however I find that the time stamp will not update when I have sheet protection on even thought I have unlocked the cell the timestamp goes in. I need to keep Protection on and specific cells unlocked for data entry. Can you suggest a fix for this? Below is the code as I am using it.

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim KeyCells As Range
    Set KeyCells = Range("M19")
    On Error Resume Next
    Set KeyCells = Application.Union(KeyCells, KeyCells.Precedents)
    On Error GoTo 0
    If Not Application.Intersect(Target, KeyCells) Is Nothing Then
        Range("L16").Value = Now
    End If
End Sub