I am trying out the client now. It runs on adobe air, so its platform agnostic (or at least it can be, it runs mac or pc at the moment).

I am surprised that it actually detected all of the games (and expansions) I had installed. Including the built in Windows games that I never use.

I didn't even know that my UT3 install was out of date, but its downloading the patch for me now.

I can't comment on the social networking stuff or graphs yet as I have only just installed it, but it seems solid so far.