States vary widely in their willingness to enforce noncompetition agreements. Some states, such as California, are openly hostile and will not enforce them, while others will do so so, subject to varying degrees of judicial scrutiny.
My home state of Illinois, for example, will enforce a noncompetition agreement, but only after fairly rigorous judicial scrutiny. Notwithstanding such scrutiny, Illinois employers can draft enforceable noncompetition agreements. The attached article that I published in the April 2009 Illinois Bar Journal offers practical guidance on how to do so.