Viral Website Part Two: Contribution

Once you have lots of people signing up, people need to get value to
continue to use it.

When it's new, there isn't that much there, so it must be easy for
people to contribute. Digg lets users submit stories, which is easy,
but even easier is to leave a comment and even easier than that is a
one click Digg vote.

The key is to figure out how people will contribute and to make sure
there is something very easy that anyone can do to add value.