One big issue with "knowledge work" is that it's leaky. Your mechanic can't take your car home and work on it at home after work hours. Once the plumber leaves your house they can't continue to work on your pipes.
Many jobs are simply done when you're outside work hours, but that isn't the realm that knowledge work functions inside. To do "knowledge" work all you need is your brain.
At the end of the day you can still think about your work. You can dash off an email with that thought from your internet communicator. Most of us have laptops or tablets that let us do our jobs from anywhere.
The dark side of the freedom of knowledge work is that it leaks into so many moments of your life that work was previously unable to claim.
This weekend I say, plug the holes in the dike between your work and your life. Live your life, without the knowledge work interfering.