We have just succesfully implemented Jumbo Frames (MTU 9000) in our envornment on UCS, Nexus and NetApp. So far we have tested, it shows a big performance improvement.
I must add we had to open a case with Cisco TAC Support because we kept having issues with QoS on the Nexus switches. Although we had configured everything correctly, we finally found there was a very surprising reason for it related to NetApp. Apparently when you configure a trunk port with VLAN tagging on a NetApp filer, all traffic coming from the NetApp is tagged with a CoS value of 4. And it cannot be changed! It took us days to discover this. So be awar of this if you run in simular issues.