It is definately this as I have just made a change to it on my test environment and it took instant effect when I refreshed the browser on my client PC, without the need to restart IIS or do anything to the server.
I'm on 7.0 MR2 but I doubt there are any differences. It is this line that I changed:
<td style="TEXT-ALIGN:right" nowrap>THIS IS THE BIT I CHANGED</td>
<td><asp:textbox id="txtUsername" runat="server" cssclass="form"></asp:textbox></td>
It appears on line 96 of login.aspx
Have you purged your browser's temp internet files? Rebooting won't do it.