Even got promoted to management in one of the two jobs! They would sometimes have to take calls from both jobs with one earbud in each ear connected to each laptop.
The industry the companies were in are not known for employing the best and brightest programmers... so I can understand being able to output enough to keep everyone happy. But it still boggles my mind that they never slipped up and got caught.
Most countries I worked in, anything done after hours, not using company resources, and not in the competition space of the employer is simply allowed. No company would be able to enforce that.
In fact (I have had that happen) if the contract tries to over reach, in particular regarding IP, then that clause could just be made void in court.