Hitwise has an interesting analyis of seasonal patterns of web traffic traffic. What I noticed was how Wikipedia use was influenced by the academic cycle.
Notice the increase in visits to Wikipedia in May (during finals) and slight decline during the summer months. YouTube overtook Wikipedia in market share in August, but as soon as school started, Wikipedia's growth outpaced that of YouTube. See this post for more detail on the Wikipedia school year trend. Not only is entertainment consumption and social networking affected by the academic year, but so is photo hosting, a tool for social networking. Visits to Photobucket also declined in September, but recovered in October. As I've reported before, Photobucket receives the majority of its upstream traffic from MySpace, making it privy to the same seasonal fluctuations in traffic. [LeeAnn Prescott - Hitwise US: Social Networking Sites Recover from September Decline, Facebook visits up 16%]