We track a large set of "rapidly" changing web pages and examine the assumption that the arrival of content changes follows a Poisson process on a microscale. We demonstrate that there are significant differences in the behavior of pages that can be exploited to maintain freshness in a web corpus. Catagories and Subject Descriptors: H.4.m [Information Systems]: Miscellaneous; H.3.3 [Information Search and Retrieval]: Search Process General Terms: Measurement, Experimentation, Algorithms