Adam Bosworth of Google has taken a look at how data is being used across the web, that is, how applications have evolved through popular usage patterns, rather than from a Computer Science view of how things ought to work, to draw lessons for application architecture. His article in ACM Queue called "Lessons from the Web" is oriented towards lessons for database design, but it's interesting that it ties in with many of the so-called Web 2.0 concepts, and I think is worth looking at and thinking about for anybody designing online applications and services.