The real point of leveraging solipsism is this:

If you can let your users do what they want to do anyway, but get some sort of emergent behaviour that is more broadly useful, then you’re on to a winner.

This is why the old corporate groupware angle so seldom took off — people won’t do things for the good of the group unless there is a distinct personal benefit to themselves. The only example I can think of where this DOES work, is the calendar functionality of some corporate email packages. The group benefit is that when setting up a meeting it is evident when the entire group is free. The personal reason to keep your electronic calendar updated, however, was primarily driven by the ability to sync Palmpilot with primary computer — people wanted to have one calendar including both the meetings arranged by email and those set up on their palms, so they synced, which allowed the group benefit.