The Exchange Team has released CU1 for Exchange 2013.
With this update it is now possible to migrate from Exchange 2010, which require that you have SP3 installed.
Besides hotfixes in the update it also new functionality to Exchange 2013, which you can read about here.
The update is in the new update format, which means that the download is a complete exchange installation, which you besides upgrading an existing installation also can install a completely fresh installation with this update. Read about the new service module here.
This update also marks the end of my participation in the Exchange TAP program, which I have been part of, for the last year, and have given me a lot of knowledge about Exchange 2013 and coexisting with Exchange 2007/2010.
You can get the update here.