With the long awaited release of Exchange 2013 SP1 on February 24th, 2014 it is speculated that Rollup 1 will be soon to follow, however Rollup 1’s release data has yet to be officially announced. SP1 resolved key issues that held up many Exchange projects including Windows 2012 R2 compatibility and the XP compatibility issues introduced in CU3. Rollup 1 will instill further confidence in Exchange 2013 as it will likely put the finishing touches on resolving bugs in CU 4 / SP1 including the transport service integration issues in SP1 (https://support.microsoft.com/kb/2938053/en-us).
If your Exchange deployment is not on SP1 yet, here are instructions for upgrading Exchange 2013 to SP1.