Only a few moments ago, Microsoft’s Exchange Product team announced that Exchange Server 2013 reached General Availability.

In short, this means that the product is now available for everyone to download and evaluate. Unfortunately, you still can only deploy Exchange 2013 in a greenfield install (no prior versions of Exchange).
However, the ETA for Exchange 2010 SP3 and the Exchange 2007 coexistence rollup was adjusted to Q1 2013 instead of H1 2013. Good news!

Read more about it in the official announcement here: