periodic beachball, activity monitor showing windowserver around 50% CPU

I upgrade my late 2009 macbook pro with dual core 3.06 ghz core2 duo and 4 gigs of ram to mountain lion and I am getting periodic hang ups with a beach ball where it goes unresponsive for 15 or 30 seconds. Not a show stopper but really annoying. I have activity monitor open and whenever it happens WindowServer cpu usage is spiking. This last time it showed 54%. Any help appreciated.