When I work on trying to create life-streaming solutions, I often get a lot of questions as to what a lifestream is and how is it useful. These questions are valid, but can be rather hard to explain to someone with no experience with social media (i.e. del.icio.us or last.fm). Even those that have used social media don't always see the problem that can arise from having content about you spread across different sites.
The first question to answer is what a lifestream is. If someone doesn't use social media, you'll need to explain a few basic types; I prefer to use last.fm and del.icio.us as examples of services because they're some of the easiest to understand. Last.fm creates a big list of music you listen to, and can help you find out what other stuff you might be interested in, while del.icio.us shares links with friends. There are more than just these two, though, one for movies, one for food, one for events, one for games, one for books, etc.
Now, at this point you have a bunch of different web-pages on a bunch of different sites: one for music, one for movies, one for games, one for events; anyone you wanted to share all of that information with would need to go to each website, figure out where your information is, then head off to the next website. Very cumbersome, even for 3 to 4 sites.
A-ha! This is where Lifestreaming comes into play. A lifestream is simply a collection of the different data from those social media websites, put onto one page. Now instead of hopping around to different sites, you can direct them to one, and only one site for yourself. This greatly simplifies things!
Usually, when I end this tirade, people nod slowly; they get it, but they still don't see how it would ever be useful or significant. I'll cover that topic later, when I have more to share.