If you don't register it, you can still use it, but it rifles through all of the days you have had it on your computer before it will give you a zip button. After you have been using it awhile, it becomes really annoying having to wait for it to finish going through the "days on your computer archive". Also, the "zip" and "unzip" buttons move around each time you use it. So it might be in the middle once, and then on the left the next time. The older program (a few versions back), still allow you to use them too without having to wait for the archive to be run through.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi