I develop software and release it under a simple license that allows people a free copy as long as it remains for personal use only. I was thinking of setting up a registration server where the software would connect, obtain a license and then proceed on. By having the user do this, I could log the IP address of the registrant and based on the amount of registrations I receive from a particular IP address, I could gauge if they were using it for personal or commercial use. I know logging IP addresses can be controversial as some people believe it's as good as a real name or home address on the Internet, or get scared if you say you have their IP address, but frankly the moment the connect to my website, Apache logs their IP address in the main log. Would logging the IP addresses of users for registration purposes contradict most privacy policies? Would this method be non-appealing to users?
If there is an alternative method for enforcing non-commercial use of a product without making legal threats or other unpleasant statements, I'd love to hear about it. This idea just came off the top of my head.