BuddyPress.org

http://1uthavi.adadaa.com/ada-wpmu-sitewide-feed-plugin/

not only has posts, pages, but also has comments for all around your WPMU installation blogs. I updated the plugin to include avatar’s of authors & many more.

I use separate feeds to display on front page [rss widget], so I can quickly check what’s my site’s activity

see at http://adadaa.com/