Here's how to get it, if you want to. And LWN has a more detailed technical description of the changes from the mainstream kernel. Basically, the kernel optimizes communication: network (InfiniBand, 10Gb Ethernet), storage (SSD, Flash memory) and memory (NUMA). It optimizes drivers and reduces complexity in the kernel (i.e. remove unused drivers and so on).
And considering the compatibility issue, here is Oracle's claim:
"Third-party applications that run on RHEL 5 should run unchanged on Oracle Linux with the Unbreakable Enterprise Kernel, while delivering significant performance and reliability improvements for end users."
Good reads are CIOupdate and PCWorld