Nigel Poulton has a great detailed writeup with all the details. I won't repeat everything here.
If you log into your EMC Powerlink you can see the release notes.
We first heard about 5875 5 months ago when VMware released vSphere 4.1. One of the neat features in 4.1 is being able to offload to hardware certain storage operations via VAAI. Chad posted the "good/bad/ugly" about EMC support for 4.1 on July 13 in 2010. Its here we learned that VMAX would not be supported for VAAI until this Enginuity release. It was certainly one of the ugly points in the post. My gut tells me that the VAAI functions probably got caught up on the code train for the deeper FAST technologies which took a lot longer.
A good thing is that with an Enginuity code update you don't need to do much work apart from contacting EMC support who then do the update remotely.
Rodos