Joshua Porter made an excellent observation a few days ago on what he calls the "del.icio.us lesson". This is the idea that personal benefit should come before network effect value - it's definitely something you should bear in mind if you're creating a social app. He writes:
From now on I’m going to call this idea the “Del.icio.us Lesson”. This is the lesson that personal value precedes network value: that selfish use comes before shared use. We’re seeing it more and more everyday in services like Del.icio.us, Flickr, and is an interesting aspect of networked applications. Even though we’re definitely benefitting from the value of networked software, we’re still not doing so unless the software is valuable to us on a personal level first. And I wonder, how will Google Base fare in light of this? What personal value are people getting out of it? Is it enough to make the service successful?
Alex Barnett gives a more concise rendering: