See: http://blogs.testbit.eu/timj/2005/07/26/26072005/ (page moved)
The user interface design newsletter from last years july has an interesting article on Adaptive Menu Design. The bottom line is:
Do not use dynamic menus (i.e. hiding or moving menu items), since people learn by spatial location.
For quick reference, and for everyone too lazy to read up on menu design, Beasts usability page menu section has a concise list of design directives to comply with for proper menu construction.