I spoke with the developers of a software package for whom I am a beta tester about this issue.
When searching on Google for information about the application I was given lots of links to illegal download sites. I pointed this out to the developers and their pragmatic answer was that they saw little point in wasting effort going after these guys or developing new security code for them to crack as in their view most of the people using cracked versions would probably never be prepared to pay for the application anyway.
The logic seems to be that they are not actually losing anything to the crackers and having more people out there using the application would not be such a bad thing!
Adobe seem to have a technically better solution for dealing with cracked software, making their software phone home every so often. Crackers disable this feature of course, but another check monitors the time since the last successful call home and if there were no successful calls after a certain period the app is disabled or switches into demo mode with the user allowed to purchase a genuine licence. Probably overkill for your app, though.