Every mouse event causes the EventTapCallback to be called, which over time results in a constant 1-2% CPU usage.

I did a basic time profile and found that the main culprit is calling [NSEvent eventWithCGEvent:eventRef], which seems extremely slow for something that I assumed would be "toll-free". There are a few things I'm going to try to reduce CPU usage in the callback, but I was wondering if you had a preferred approach.