It's been a non-started for a couple of companies, but if that's the case, I don't want to work for them anyway.
Once I worked for a company, and me and the owner had a disagreement that wasn't resolvable so I said that I'd have to quit. She leaned back, smirked, and said, "remember that you signed a non-compete." I simply replied, "No, I didn't." She suddenly had an "oh crap" look on her face and looked at the HR director, who said, "I thought I'd get him to sign it later so we let it slide when he came on." The owner then tried to stop me from leaving, but after seeing that shark smile on her face I knew it was only a matter of time before she found another way to screw me and left anyway.
There are more of us than there are them. We all need to stop agreeing to these clauses.