Depends on scope. I had to sign one at my current job, it stipulates that i will not work for another Sage reseller within 50 miles within 6 months of ending my employment. That is sufficiently narrow that it was a no brainer - I was not a Sage consultant before taking this job, my current employer is the one who has provided and paid for any Sage specific training I have had, and I am not barred from seeking other IT employment that doesn't deal with Sage.
Were I a Sage consultant beforehand, I might have thought differently. Several of my co-workers did, they are 1099 contractors working under their own LLC, and are not subject to a noncompete, but they also don't have access to the same health benefits, and they likely pay higher taxes as a 1099 employee than a W-2 employee (unless they make considerably more than I do).