Microsoft is working to improve the features and range of the Federation (and public IM) functionality in the future releases of the product.
Microsoft has announced that they will be working to widen the range of Partners in the public IM cloud that OCS can connects to, and also to remove the need to license the Public IM connectivity.
On the question about connectivity to Skype, MS has answered that it is not Yahoo!, AOL or MS that is blocking for this option. ( i believe that Skype is unable to integrate due to the design of their P2P Voice client software)
I think we will see improvements in the near future, maybe already when OCS 2007 R2 goes RTM.