I've just posted a new video about building aggregations in SSAS 2008 using the new aggregation wizard. The video discusses:
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• How to create aggregations in SSAS 2008
• The aggregation wizard, including the new Aggregation Usage page
• The "one-third rule"

The video shows you how to run the wizard and the choices you have to make. This video runs 25 minutes.

This video, along with all others, can be found on the Videos page of the site.