look no further other than KB2892464. As usual it contains several bugfixes, support for IE11 in OWA, less memory consumption for the search infrastructure, bug around backup and restore which you can read more about in KB2888315.
To install CU3, you must deploy schema updates so talk with your Active Directory team to have them deployed before you run the CU3 setup.
Download is found here
Microsoft also released Exchange 2010 SP3 UR3 which can be found in KB2891587 and download from here
As always, read the KB and notes carefully before deploy.