As Long As You Didn't Sign a Non-Compete It's Fair Game
I recently started to do work as a contractor for my brother's business. In 10 hours of work I made more money than I make working 40+ hours for my employer. I don't "fix computers" anymore because people expected a discount price for a premium service ("Upgrade my memory and clean my spyware for $30, please!"). I'm strictly limited to s*** worth my time and effort. I charge $120/hr for Enterprise Support for small businesses.
Why? I like the extra money and I get to work with technologies that I normally wouldn't get to work with. This makes me more valuable to my employer since I have gained experience outside of the workplace that I can apply in the workplace.
A wise man once told me:
"Find a job to support your family and find a job to support yourself."
How true. Some people can find a job to support both, but my side job pays for all my toys. My wife doesn't see that money and can't complain that I'm spending our money on useless stuff.