[bluGill]

Note that if the copyright is registered before hand the infringement occurs actual damages changes to triple actual damages. (In the US) registering a copyright is cheap, but for software you have to register each version separately which adds up quick. You have to register copyright before you can sue for violations in any case.

Most of the time lawyers advise the policy that you don't register until you are ready to sue for a violation. You only get actual damages but this is typically enough. However if you believe someone is actually going to violate your copyright (or you want to spend $25 + plus lawyer fees) you should register before you release software: you will get triple damages.

I'm not sure what damages means in terms of the GPL though. In the case of a book you can say the book sold for some amount of dollars so every sale of your illegal copy cost me that amount of dollars.