That type of daily behavior is common in human activities. It matches nicely with typical daily activities like waking up, having lunch, etc... See http://www.bgoncalves.com/component/jdownloads/finish/3/17.h... for an example in web page traffic, http://www.barabasilab.com/pubs/CCNR-ALB_Publications/200805... for cell phone traffic, etc...