The update contains many security enhancements and other improvements. New security features include Exec-shield and PIE (Position Independent Executable) features, which provide some first rate protection against various stack, buffer and function pointer overflows. Red Hat has also "extended NX (No Execute) support from the Intel Corp. Itanium2 processor family to include other chips that can be made to support it such as the Intel x86, Intel EM64T (Extended Memory 64 Technology) and the AMD64 processors."
The update also features Ximian Connector, which is a software tool which can be used to connect Linux based e-mail clients such as Ximian Evolution to a Microsoft Exchange server. The Linux clients appear just like Outlook clients do. All in all, some great tech from Red Hat.