He comments on Clay Shirky's "Situated Software" (which I have acknowledged earlier) and says:

One reason the situated software approach works so well is the clear definition of the end users of the system. It enables developers to build for a very specific set of users and features, which is a wonderful foundation for success.

Excellent point: a situation is or is not present at any point in time, and if it is, it is very clear what the problem is the user wants to solve in this particular situation.

This obviously requires a good "situation matching" algorithm, a point that Clay does not really deal with.