Nice post from Technology Review giving a nice plain English primer of what the Activity Streams open standard is trying to achieve. Hopefully at one point it will provide an easy way to seamlessly create lifestreams and provide unique functionality with the associated data.
From the post
The standard, known as Activity Streams, aims to solve the problem that FriendFeed–acquired by Facebook a year ago, but largely stagnant since then–was supposed to fix: bringing together what your friends are doing from all over the web. They may be posting pictures to Flickr and Picassa, microblogging at Twitter, liking things of Facebook, recommending articles at their favorite news sites, etc. It's a firehose of information that you should be able to filter intelligently–and, more importantly, add to as easily as you add a new RSS feed to your reader or a new mailing list to your email inbox.