Sometimes when I click on the wifi icon in the menubar it starts beachballing and then all the system icons on the right size freeze and give me a beachball too. Other icons from apps I have installed are fine and so are the buttons on the left. No way to fix it other than logging out/rebooting. Killing the menubar in Terminal fixes it until I go click the wifi icon again. This is happening on my rMB on 10.10.3 and is kind of random.