Yahoo Groups is one of the most active social networking places in the internet – serving millions of users for years even before facebook and myspace. I think Yahoo Groups has still a high potential to evolve as a user loving, social feature rich application to challenge the facebook era of rival sites.
The challenge here is how to make users visit the site often when they can use most of the group feature via email? Yahoo recently started introducing the concept of applications in groups, which hopefully make users realize the power of the additional features from the web interface.
Yahoo stopped the beta testing of the new interface some time back. They promised more features to the existing platform, which seems to be working with the added applications section and other new features.