In California, judges do laugh at them, because the vast majority of US non-compete agreements would be unenforceable in California. Employees can be prohibited from using trade secrets from the job after their employment is ended as you say, but the "non-compete" itself as generally described can only be enforced in the case of a business owner who sells his business, and "its good-will" (edit: and the good will is revokable and must be spelled out and compensated.)
The assumption underlying the exception being, last I heard at least, that if a business owner sells their business to you, there is an expectation that they are doing it in good faith, and they will not intentionally undermine the success of the business that you bought. It would be "in bad faith" or faithless for that former business owner to go out and round up all of the customers of your business, and start marketing at them new contracts with a new competing company that does just what the company you purchased does.
This is, to my knowledge, only really the law in California (non-competes are mostly enforceable in other states), but my understanding is that if a person from another state has some other kind of non-compete agreement that they wish to escape, they can also do it safely by moving to California and going to work for a CA employer.
My ailing memory tells me there was a third different condition in which non-competes were able to be enforced in CA, but that it was also very narrow and unlikely to cover a regular former employee, or ever prevent them from working for a competitor... if anyone knows the law better than I do, feel free to chime in with whatever I'm missing.
I think I remember that the "good-will" clause needs to be spelled out explicitly, in terms of a period of time and a specific compensation that it is tied with... that might be what I had forgotten.
The good-will is revokable and the penalty for revoking it can be no more than the specific compensation associated. I seem to remember actually, that the good-will compensation must be structured as a series of payments, because the penalty for revoking your good-will is actually just the discontinuation of those payments, not a statutory damage or requirement of returning any of that money that was already paid.
IOW California judges will usually just laugh at non-competes. I think I also remember that there is a statutory damage amount that employers must pay, if they write and attempt to pass any overly broad or non-enforceable non-competes as a condition of employment.
IANAL though, of course ask your lawyer if you really needed to know...