Comment Partial Key Verification (Score 3, Interesting) 635
This is something that I have never dealt with directly, but I saw a similar post on StackOverflow a few months ago and bookmarked it because it seemed useful.
The answer it seems is something called "Partial Key Verification": http://stackoverflow.com/questions/3550556/ive-found-my-software-as-cracked-download-on-internet-what-to-do
In short, the software would still work, but re-direct people to a page letting them know that they've been "caught" pirating software and that they should really purchase it. This won't stop everyone, but some people (especially in a business environment) won't risk "being caught", so they will purchase the software knowing that you know that they know they are pirating your software.