In my opinion, if you don't know exactly how you will protect your source code efficiently, then don't start trying to hash something together yourself based on hardware. It will be too easy to break, and most likely just annoy your customers.
I would sugest you have a look at how Atlassian does this. They happen to sell Java software, and apparently do quite well. http://www.atlassian.com/ Try downloading e.g. JIRA and play with an installation. This will give you a good idea of how their licensing scheme works, and what users can reasonably expect from professional software.
