I wrote up proposal for a design pattern of short listing that helps alleviate the inherent tension that Activity Streams can create by showing content only for limited periods of time. 

The original blog post is found at http://corvusconsulting.ca/2009/11/activity-streams-ephemeral-data-and-the-short-list-pattern/ and discusses an early implementation in Gnolia.com. Feedback on the pattern's applicability to activity stream design would be much appreciated.