1. A method comprising: monitoring, using a computer, forum activity in a selected group of online forums accessible over a computer network, wherein the forum activity is caused by contributions from a plurality of clients participating in the online forums; generating an index of forum activity measurements comprising activity measures for each of the online forums, using the computer; receiving a data request for forum activity measurements pertaining to one or more online forums included in the group of online forums from the index; and serving the forum activity measurements from the index in response to the data request.