Exchange Server 2013 on Windows Server 2012
Unless you've been living under a rock, you know that the public betas of all the Wave 15 products, including Office, Exchange, Lync, SharePoint, etc. were released earlier this week as "2013" products. These were all released on Monday July 16, 2012. This follows by a couple of weeks the "release previews" of Windows 8 and Windows Server 2012.
You can download the Exchange Server 2013 public beta/preview here.
In the original release, it was not supported to install the Exchange preview on the Server 2012 preview. Today, Microsoft has changed that guidance and now supports installing Exchange Server 2013 on Windows Server 2012.
At this time, it requires a couple of additional manual steps. You can find information about how to install Exchange Server 2013 on Windows Server 2012 here.
We can reasonably expect that this will be cleaned up before RTM.