All of the major ranking sites - including Alexa, comScore and HitWise - hold considerable influence and weight for both website owners and advertisers. However, Web 2.0 sites use certain technologies that can make ranking them difficult, sometimes shortchanging the sites and their influence or earning potential.
ComScore has announced a new set of metrics that will take 2.0 sites into account. In particular, AJAX and similar technologies have the ability to add new information to a page without refreshing, hence not accounting for a new page view. On the other side of the coin, a site like MySpace is designed to load page after page whenever navigating the site - accounting for many page views and what some say are inflated rankings. While MySpace is built to generate page views, newer sites are built to minimize page views for a better consumer experience. With old ranking systems, this puts certain sites at a great disadvantage - even though those sites may present a much better user experience.
It's a little odd that it has taken this long for Web 2.0 sites to be viewed differently by ranking systems than their older, more established bretheren, but it's certainly good news for community-enabled sites.