Applications integrated with OCS to leverage the power of presence is really good news for everyone. Customers using Dynamics GP 2010 can see the presence of contacts within the product. Obviously it requires Federation to enable cross business presence but this is a great driver to bring even more emphasis on B2B unified communications.
Below is screen shot from the Microsoft Dynamics GP Product blog which also discusses the features in a little more detail. http://blogs.msdn.com/gp/archive/2010/03/30/feature-of-the-day-unified-communications.aspx