We've got a collection of posts on our weblog that are great resources for tweaking ClearContext to get the most out of the product. See the following:
Archive Sent Messages in Outlook
ClearContext Prioritization Adjustment
ClearContext and ActiveWords: A Script to Get Started
Convert Your Folders to Topic Folders
IMS Pro Tips
Vacation Email Triage
How to Avoid Exceeding Your Exchange Mail File Size Limit
Outlook Performance and Mail File Health
User Guide
If there are other tips and tricks you'd like to see here, let us know.
[7.30.06 - Updated to reflect new tips]