I sell a Mac app, which performs periodic update checks, so I can estimate how many users I have. The update checks also contain info about whether the product is licensed, and whether the code signature is valid. I assume that copies of the app that say they are licensed but don't have a valid code signature are cracked.
Here are my numbers from July:
13301 trial users
4934 paid users
367 pirates
If I look at these numbers, I don't see why I should bother doing anything about pirates. Any effort spent on convincing pirates to pay is better spent on convincing trial users!
(PS: the update check can be disabled, and I don't know how many people disable it, so the above numbers are rough estimates at best. Also, invalid code signatures might be caused by things other than piracy eg. software bugs)