A pretty esoteric topic, but you never know when some of these features may come in handy. I have picked out some that I think are most useful, but there are plenty more listed in the documentation (You read the documentation, right?)
Outlook 2007
/cleancategories
Deletes any custom category names that you have created. Restores categories to the default names.
/cleanclientrules
Starts Outlook and deletes client-based rules.
/cleanfreebusy
Clears and regenerates free/busy information. This switch can be used only when you are able to connect to the server running Exchange.
/nocustomize
Starts Outlook without loading outcmd.dat (customized toolbars).
/sniff
Starts Outlook, forces a detection of new meeting requests in the Inbox, and then adds them to the calendar.
Word 2007
/a
Starts Word and prevents add-ins and global templates (including the Normal template) from being loaded automatically. The /a switch also locks the setting files.
Starts Word and opens an existing XML document based on the specified XSLT
OneNote 2007
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