Do you know what VMWare vSphere version you're running? If its 5.1 or below, it's time to think about upgrading so you don't lose support.
Last week I went into a customer environment to talk about infrastructure planning and found that they were on an old 4.x version of vSphere, which went end-of-general-support back in 2014, yikes!
This was an important reminder to me that VMWare vSphere 5.1 is next up: going end-of-support in less than a year, on August 24th, 2016. Those of you on VMWare vSphere 5.5 are still good for a while, with support available until September 19th, 2018.
Check your version's end-of-support date on the VMware Lifecycle Matrix:
Once you've done that, then you'll need to verify that your server hardware is on the support matrix for the version you're upgrading to (or at least for 5.5 right?). You can find that information in the vSphere HCL Compatibility Guide:
I know my customers with G6 servers are not supported for anything newer than 5.1, so it's time to plan a hardware refresh as well.