4. The method of claim 1 , wherein the event data reflects orders placed by users for items represented in the electronic catalog.
1. A computer-implemented method of matching users to user communities, the method comprising: for each of a plurality of users of an electronic catalog, storing event data representing user-generated events that reflect user affinities for particular items represented in the electronic catalog; storing information about a plurality of user communities, each of which corresponds to a respective subset of the plurality of users and comprises multiple users; identifying a first plurality of items that characterize item preferences of a first user community of the plurality of user communities; calculating a degree to which the first plurality of items are related to a set of items in the electronic catalog identified by the first user; and based at least in part on the degree, determining whether to suggest the first user community to the first user; wherein the method is performed by one or more computers.