Released today, Exchange 2013 RTM CU1 is now publically available for download. You can now co-exist with your Exchange 2007 SP3 RU10 and/or Exchange 2010 SP3 environment. You can also start to deploy and migrate users to the new Exchange 2013 platform. So have it. Start in your lab, test your environment applications, and then plan your production move.
Exchange 2013 Deployment Assistant: http://technet.microsoft.com/en-us/exdeploy2013/
The Exchange Remote Connectivity Analyzer (EXRCA): https://www.testexchangeconnectivity.com/
Exchange Team Blog site: http://blogs.technet.com/b/exchange/
Premier Field Engineering Blog site: www.mspfe.com