In the Form_Unload event handler, save the text using SaveSetting.

' Load the saved value from the registry.
Private Sub Form_Load()
    txtPersisted.Text = GetSetting(APP_NAME, SECTION_NAME, _
        "txtPersisted", "")
End Sub

' Save the value in the registry.
Private Sub Form_Unload(Cancel As Integer)
    SaveSetting APP_NAME, SECTION_NAME, "txtPersisted", _
        txtPersisted.Text
End Sub