License keys are fairly useless in my honest opinion.
What's to stop your customer from distributing that key to others? Sure you could setup a license key server that records the number of activations but that costs money and what will happen if it goes down or goes away?
In my professional opinion, create a software that is branded uniquely to a user (encrypted inside the program of course). For example, if you goto help -> about of the software then display the person's name, phone, and possibly their address. This way if they upload it to a pirate site of some kind, not only will other people know this guys personal information...but so will you in order to charge him for more licenses or sue him.
