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The out of the box activity feed of SharePoint can be extended with custom activities. These activities will then also show up in the My Newsfeed on the My Site.

http://weshackett.com/2011/06/extending-the-activity-feed-with-enterprise-content/

http://msdn.microsoft.com/en-us/library/ff426881.aspx

http://www.nerdonarock.com/2011/11/03/adding-custom-activityevents-to-the-newsfeed-with-activitymanager-and-event-receivers-in-sharepoint-2010-mysites/ 

http://bramdejager.files.wordpress.com/2012/05/extending-the-my-site-activity-feed-with-external-blog-posts-bram-de-jager-sharepoint-saturday-2012.pptx