Measuring open source adoption is a perennial problem. How do you compare "products" that don't have sales figures? By aggregating the web sites that a large number of people visit, you get some objective measures that can show trends and behaviors.

Because of the extensive sample size of network data, Hitwise can give detailed insights into the search terms used to find sites as well as analyzing the movements of visitors between sites.

This data is usually used to devise and benchmark marketing campaigns, but it can also be applied to other weighty battles, like PHP vs Perl, MySQL vs PostgreSQL, or Slashdot vs Digg.

The perennial arguments will probably continue, but everybody loves numbers in arguments.