Patent 5,636,276 will be expiring in 2015, assuming my math is correct. The patent, which covers distributing music digitally, has been used very effectively to get royalties from many companies, recently Spotify when it came to the U.S.
My thinking is that if the patent can be used this effectively against large, successful companies, then after it expires it can be used to protect small companies and individuals.
I imagine there must be some process that a developer should follow to be sure he or she develops the product such that it can be protected if sued by owners of similar patents.
What would that process be?
Edit: I'm not looking for a step-by-step description using this patent (it's just an example), just the requirements that a court would look for when evaluating whether or not the product is properly using a public domain patent.