Today we announced the availability of the first, and possibly only, Exchange 12 Community Technology Preview (CTP) build. This build is available to Technet and MSDN subscribers only which equates to around 200k+ users.
This version will run on a 32bit operating system and hardware so feel free to download and have a play.
Most worth noting is that fact that because it's based on the private beta code, anyone testing it is still under NDA and should therefore a) not share the build b) discuss features that may or may not work that have not yet been publically announced.
If you are not a Technet or MSDN subscriber then all you need to do is wait until the summer when a public beta will be made available for anyone to download and try!