I started having an issue on my Linux box on which I normally do development where my desktop was virtually unusable while Eclipse kept the CPU pegged. Adding to the mystery was that a full 20% of the CPU usage was system time. After restarting Eclipse several times, clearing out cached files in the workspace/.metadata, rebooting, etc., nothing seemed to help; as soon as I started Eclipse it went nuts again.
So, we have a MacBook Pro we use for a family computer that I commandeered for work. I plugged it into my large screen and plugged in my USB keyboard/mouse from my Linux desktop so I could continue to work in a relatively familiar environment. After a while, I noticed that one of the cores on the MBP was constantly in use. I discovered the offending process was "UserEventAgent".
After searching and finding several articles about this, I eventually followed the apparently benign step of moving the /System/Library/UserEventPlugins/AppleHIDMouseAgent.plugin directory out of the UserEventPlugins directory, and rebooted. When I restarted, my CPU issues were no longer. It sounds as though it's an issue with several external keyboards, although I happen to have a Kinesis keyboard as specified in the link.
Then, to complete the irony, I switched back to my Linux desktop, and the previous performance issue with Eclipse appears (for the time being) to be gone. How I love technology... #performance #macbookpro #keyboard