Same here. Also I sometimes think about these kinds of things when I'm off the clock too. I don't want to but you can't exactly tell your brain to stop thinking about work stuff at 5pm. Sometimes I'm just watching TV or whatever and a thought about how to solve a work problem pops into my head.
To me it says more about how bad the management is at a company that has to resort to try to detecting mouse jigglers. Do they know so little about what the employees do that they don't simply notice that work isn't getting done if an employee isn't actually working?