Exchange 2010 SP3 RU7 has a handful of bug fixes, and so far is rather unintersting and uneventful.
Exchange 2013 CU6 on the other hand, has had a couple major issues. The first issue only happens if you're in Co-Existence with Exchange 2007 and have a Database Availabilty Group (DAG). After installing CU6, Databases in your DAG may failover unexpectedly. An interim update is available to fix this issue. You'll have to contact Microsoft Support to obtain it if you need it.
The second issue only happens if you're in a Hybrid deployment with Office 365. CU6 includes the fix for KB2988229 where running/rerunning the Hybrid Configuration Wizard would fail in CU5 or earlier due to a change made on the Office 365 side. Great news! Except that it breaks some basic functionality for your Hybrid deployment, like creating a mailbox. There's a script to fix this, but the script will fail if you've installed Exchange anywhere BUT the default install path. You can fix it by changing the baseDirectory in the script (found in 3 spots) to this: $baseDirectory = "$Env:ExchangeInstallPath" + "ClientAccess\ecp\DDI"
Josh M. Bryant is currently a Director of Technical Product Management at Tanium where he builds products that help customers overcome the challenges of managing very large scale computing environments. Prior to joining Tanium, he was a Premier Field Engineer at Microsoft specializing in Microsoft Exchange Server, and then later a Cybersecurity Architect specializing in Compromise Recovery.