I see a lot of questions on interoperability with Cisco and Microsoft on the TechNet forums and just wanted to highlight a great resource available from Cisco. The Cisco Interoperability Portal has a great deal of documentation on integration for both OCS and Exchange from Cisco environments. It also has documentation related to Avaya and Nortel and interoperability to gateways and number of other Cisco products.
Cisco Unified Presence is probably the most confused and talked about topic of all in regards to OCS and interop. Although I must admit the configuration is not all that straight forward the document available at the portal will give you the basics to get started in a mainly screen shot format.
It’s not what you know but whether you can find it when you need it.