Mac Editor: Constant High CPU Usage

Hi, I'm using the Unity 3.5.5f3 editor on Mac 10.8.1 and I'm seeing very high CPU usage even when Unity is in the background doing nothing.

I emailed support about it but they've been useless; after two weeks they sent back an "unable to repro" reply. I asked if there were any logs or debug files I could provide them to help them reproduce it, and they never got back to me. That was weeks ago.

Anyway, the behavior I'm seeing is that with the editor open, the Unity process routinely uses between 65 and 70% of my CPU. This is when I'm doing absolutely nothing; it happens even when the app is in the background. It also happens when I close both the Game and Scene tabs, so I don't think it's got anything to do with rendering a large scene.

When I switch to a blank scene the CPU usage drops to what I believe should be the normal level: 5-10%. So something about having a normal game scene (not a particularly complex one, frankly) open is causing my CPU to constantly churn, which usually kicks my fans in as well.

I'm using a few plugins, with uScript and ProBuilder being the two most prevalent.

Has anyone else seen this? If so, do you have any suggestions? If not, can you think of any troubleshooting steps I could take to try and isolate the issue?

Thanks!