I’ve said it before, but must say it again– Alexa, Compete and Quantcast are not serious tools for analyzing web traffic. However, they are useful for comparing sites in the same basic genre, and for looking at the growth of various sites over time. According to Alexa, Digg peaked sometime in late 2007, and has been slipping ever since. Compete and Quantcast show modest gains since late 2007. Which is right? Probably both– Digg’s core audience is over-represented in Alexa’s numbers, and some of them have moved on to other sites, others have gotten older and have less time to spend on the site, and for some the novelty has probably worn off. The slight gains that can be seen on Compete and Quantcast mean that Digg is reaching more mainstream users, which is a plus. However they must be somewhat worried that A. they’re not growing that fast and B. the core demographic appears to be slightly less crazy about the site then they were last year.