Here is my bit.
72 hours within being fired/quiting, they can't compete. Period. 6 months, they can't work for or with or clients after termination. There are exemptions, I.e. they work for someone else, but didn't bring them the lead.
While working for me, if they work on someone's computer, its either for free and not representing the business in any fashion, or they do it as part of the company. Not going to have someone mess up a computer on their time and it come back on my business. If they visit one of our clients, they represent us, not their wallet.
There is an area restraint, its basically what we consider to be our primary area.
Like motz said, don't make it overly restrictive. But do keep in mind, some techs get this thing in their head they aren't making enough, and go around doing work for extra cash. He shows up wearing your shirt, or the client knows he works for you and the employee screws up something, it comes back on you. Some employees also get approached by dirty businesses where they are paid for a client list and what the costs for services and coverages are for those clients. Its hard to prove, but if your employee leaves and all of a sudden half your clients follow, there is something up. Same with employees who leave and start their own business.
Oh, and grab a lawyer. Templates are great, but laws vary state to state, county to county.