I have been using a system called Twine recently with OK, but not awesome results.
I think the concept of Twine is good, but the user experience is somewhat underwhelming. It is a comprehensive solution and I actually think it has the right feature set. The problem is that like usual, comprehensive adds a lot of complexity and that is where the failure comes in.
Twine kind of tries to have a Web 2.0 look and feel and although that works for low-feature applications like Twitter, it really fails with complex systems like Twine. The system is just crying out for more richness and sophistication. I would love to see a more dashboard view of all the information that is added to my areas of interest and a better way of showing recommendations for new Twines.
I am still using the system, mostly because they have been able to attract some real interesting people, but I think they are going to have to do a lot of work to go mainstream. It is a shame, because if they did do a face lift, I think they could be a main player in the next shift of the Web.