Steven Greenhouse reports in the New York Times that noncompete agreements are popping up in jobs and businesses where really they serve no legitimate purpose: Noncompete Clauses Increasingly Pop up in Array of Jobs. A couple of examples of jobs where noncompete agreements have been used to prevent an individual from going to work for another employer: summer camp counselor, yoga instructor and pizza cook.
Noncompete agreements do have a proper but very limited role. Certainly with regard to protecting what can truly be considered a trade secret and other very limited circumstances, they are properly used and and should be enforced. But these circumstances and the jobs and industries in which they arise are limited.