The master Category list is part of each user's Windows registry. Users can
see what categories other users have put on items, but don't know what
categories the other users have on their master lists. The best solution in
a public folder is to enforce category selection through a custom form, such
as the sample form from http://www.outlookcode.com/d/forms/reqcat.htm . See
http://www.slipstick.com/outlook/olcat.htm for more info.