Well over a year and a half ago, Joe Gregorio made a connection between the Web and stigmergic systems. I've been thinking about del.icio.us as a potential example of the same principles: many individuals being completely selfish, coordinating through changes in a "physical" environment, to create a complex physical construct.
Looking closer at the definition of stigmergy, I think the analogy is not apt. The concepts of stigmergy have two assumptions that break down with Web systems. First, conceptually any individual in a stigmergic system can modify any bit of the environment. Clearly, everyone doesn't have the right to modify any web page. Second, in all of the biological and alife examples I've seen, there's been a Euclidean space that constrains the actors actions. As a network, if you use links as distance, you don't have a Euclidean space.
These issues may not be showstoppers, but if you want to model action on the Web as a stigmergic system, the translation is not a one-to-one mapping. It may not matter though, as this meme has seemed to die out. Probably better off going back to games on graphs as I first encountered them in Duncan Watts' work.