Described is a technology by which forum web pages are processed into clusters for classification purposes, including by determining repetitive regions between pages and associating pages that have similar repetitive regions into a common cluster. Patterns corresponding to the regions are determined, and a feature set based at least in part on those patterns (e.g., pattern frequency) is extracted from the page. The feature set of a page is compared against the feature set of another page to determine similarity therewith, e.g., via a feature space distance computation that is evaluated against a threshold distance.