The functionality set looks good. The UI is pretty good - I find the initial color set to be a bit jarring but they do make the CSS available to you which will allow folks to really customize their profile page. So congrats on a nicely designed, functional network!
Maybe I'm in a grumpy mood because Brandon Hall got rid of their Yahoo Discussion Groups to provide this network. The network UI is hardly "nicely design and functional." It will take you a while to understand what you are doing and where you go to do what. Part of the issue is that there's not much content today so it feels a bit hollow.
Part of my reservation is that it is yet another social networking tool and a blogging tool. Do I need to use it in addition to Linked In and Blogger? Part of my reservation is that unless it achieves a large number of active users and displaces existing means of community, then it won't hold enough value.
Maybe I'm grumpy and missing the point? But my guess is that this is going to be a big failure.
Am I wrong? What does Mark see?