Sam Arbesman has written up an initial analysis (PDF file) of the results of the Memespread Project. In discussing the spread of memes, it's common practice to utilize familiar biological terms: viral, epidemic, contagious, incubation, etc. My favorite quote of the article along those lines is "Jason Kottke is an informational equivalent of Typhoid Mary". Heh. But in this case, MetaFilter turned out more Mary than I:
What seemed most interesting is that the largest spike occurred 10 hours into the experiment, and was due to the website MetaFilter (http://www.metafilter.com). The spread of the meme to this collaborative blog seemed to help give the epidemic another wave of spreading (as can be seen in Figure 5 and Figure 1).
Because of its greater traffic, MeFi exposed more people to the meme than did kottke.org. And I suspect that due to the different audiences of the two sites, the meme was probably also more virulent among MeFi readers than kottke.org readers; that is, MeFi readers were more likely to infect others with the meme than were those of kottke.org.
It would be interesting to run this experiment again under slightly different conditions. Maybe seed a bigger node in the network (MeFi instead of kottke.org). Or seed 50 sites at the same time, each with a different meme marked with a distinct tracking code (e.g. www.example.com/?id=47) and see how each one spreads. Maybe the memes could be mutable; creating a new strain would be as easy as adding a couple digits to the tracking ID.