Got this in my e-mail this morning:
Activate your free mobile add-on licenses before April 20th!
Dear Unity Developer,
Our free giveaway campaign of Unity Mobile Basic add-on licenses for iOS and Android has generated a lot of new excitement in the Unity community about the great potential in developing a mobile game. We would like to remind you that if you have downloaded more than two free Unity mobile add-on licenses through this promotion, you must activate them no later than April 20th, 2012. If you activate more than one license on the same computer, only the last serial number/license activated will be valid. Here is how you can activate your licenses:
So don't forget, otherwise you'll be stuck paying for it if you want to use it, and who knows with Unity will run another sweet promo like this.
PS: I, myself, grabbed like 5 licenses for the Android and iOS... but as the e-mail says, it's only going to activate the last serial you enter. Any ideas how to get around this? I'd like to keep them active until the summer when I have a summer project planned with some coworkers. I guess download Unity on to as many computers as possible and activate the licenses?