I might conceivably use one for a formal report, but never for an email or casual note - and most of my notes are casual. The first thing I figure out in any new software is how to turn that bullcrap off.

Tools->Spelling and Grammar
Select the Options button
Uncheck the "Check spelling as you type" box
Uncheck the "Check grammar as you type" box

I haven't had that exact problem with the french date, but this should completely eliminate MS Word's innumerable helpful suggestions. Now, if you help me locate the "stuff this up Bill's backdoor" switch, I'd be very grateful.