VBA, Excel - ScreenUpdating

Typically, when I author macros inside Office, I set...
Application.ScreenUpdating = False
...when my macro starts and set it back to True when it ends. This reduces screen flicker for the user and speeds up the macro. This has worked in the past (Excel 5), but doesn't seem to now. I have Excel 97 at work and Excel 2000 at home. In both places, if I set the value to False and check its value immediately after that, it still remains True. No matter what I do, I can't seem to get it to go False.

Any ideas why?