The new Lync Server 2013 and Exchange 2013 has now been made available to all MSDN users.
I have been working with Exchange 2013 the last 8 months as part of the Exchange 15 TAP program, and I must say, it is a cool product, and I am looking forward to tell and learn my customers about the new features.
The upgrade process of the customers will begin in the first half of 2013 when Exchange 2010 Service Pack 3 is released, which is a requirement for co-existing.
The Exchange 2007 upgrade process is not supported yet, but will also be supported in the first half of 2013.
The RTM version of Office 2013 can also be downloaded from MSDN.