I found the demographics released with the report even more interesting than the traffic numbers:
For the four weeks ending August 5, 2006, 59% of visits to Del.icio.us were from males, and 41% of its visits were from those between the ages of 25-34. That's a very large skew towards a specific age group, and del.icio.us also has a large skew towards users with household incomes between $100k and $150k per year - 36% of its users fell into this income bracket, compared to 13% of the online online population.
So who are these 25-34 year olds with incomes greater than $100k per year, and why are they using del.icio.us? Claritas PRIZM NE segmentation of the site provides some clues. For a full explanation of the segmentation methodology, visit this post, or the Claritas site. What the chart below shows is that del.icio.us is highly skewed toward the social groups U1, "Urban Uptown," and S1, "Elite Suburbs." Members of these social groups have higher than average incomes and tend to be highly educated and are more likely to be early adopters of technology. My guess is that they've heard about del.icio.us through news media or through friends and are using it because it's 'the thing to do.' This is not quite the MySpace crowd that I expected to find - instead Del.icio.us users are a more sophisticated breed of web power user. (Hitwise)
It would be interesting to compare the del.icio.us demographics with those of MySpace, Digg, and a few other web 2.0 sites.