>My officemate needed to add a primary key to an @10,000 record database.
>He added PKEY a DateTime field.
>He figured, since users add records by an Add button, then fill in the rest; Replacing PKEY with DATETIME() on add is fine. I wonder if that is enough.

You should use an integer as a primary key... you are taking too much of a chance that a user will not hit save at the same time. This is really an unnecessary risk.