I like the opinion of Mason Wheeler best. This is the shortened version:
… Only a perfect licensing system would actually do you any good, and there’s no such thing. And in the age of the Internet, if your system isn’t perfect, all it takes is for one person anywhere in the world to produce a crack and upload it somewhere,
…
If you want people to pay for your software instead of just downloading it, the one and only way to do so is to make your software good enough that people are willing to pay money for it….
But if you insist on running the rat-race against the internet of crackers or your software is in such a niche that cracking is more costly than paying for a license: Tool for licensing and protect my Delphi Win32 apps – Stack Overflow
–jeroen
The Wiert Corner - irregular stream of stuff 