I was just skimming through the new KB articles and noticed this one “Verify the health of ESX Server Operating System“:

There are many ways to look at ESX host performance. This article focuses on quick assessment of the 4 main resources:

• Disk Space
• CPU
• Memory
• Network

The article refers to different KB articles for pinpointing and solving performance related problems. I suggest you add this article to your bookmarks cause it probably be updated on a regular base!