I experience significant lag/lock-up when my Publish Services menu is expanded. The animation of the menu itself, as well as the other visual functions oF LR. If the menu is already open, the other parts of the display scroll properly, and no other functionality is affected.
Win7 Ultimate / 6-core AMD / 8GB ram. I do have my catalog (75k photos) on a different drive than the app, but they all have 5GB+ free space at all times. This problem began for me in LR4, and even after having removed publish services, reloading individually, and reinstalling LR, upgrading to CC, my system is hobbled if I try to interact with that region of the Navigator. The functions themselves are fine - uploads, etc. run smoothly. It seems to be a UI thing.