I saw this the other day and I was pretty amazed by the simple and yet so easy to use activity stream that could work for Buddypress. Didnt really know how to put it here so check out this video:
<iframe src="http://player.vimeo.com/video/33183902?title=0&byline=0&portrait=0" width="400" height="225" frameborder="0" webkitAllowFullScreen mozallowfullscreen allowFullScreen></iframe><p>Touch from Gordon Evans on Vimeo.</p>
Could this be realized as a plugin for Buddypress?
Just sharing my thoughts!