I'm curious, does this ever snowball into a bunch of people emailing in with hardship stories asking for free licenses? It seems like it would, and that's the standard counter-argument: "If we give it to you, we have to give it to anyone, and once people realize that licenses are free if you email us, we'll never sell another copy."
I've done this for four years. People never seem to catch on, most of the people who email for free licenses are downright apologetic about it, and in four years I've only felt like I was being taken advantage of maybe twice with regards to free copies. (And I gave them, of course.)
Explicitly asking for something in return would probably be a good idea for me. Most of my customers tell me that they'll tell their friends, which makes me happy but empirically does not do much for the business since they're going to tell a single digit number of people who have no money, and the conversion on that is terrible. I should really tell folks that I'd love if they mentioned it on their class homepage or something.
The awesome thing about running your own business is that you don't have to do anything if you don't want to.
I make a point of giving out free Twiddla subscriptions for educational uses (on the assumption that students eventually become young executives who have to sit in a conference room while people in suits waste an entire hour trying to get WebEx to work at all, and might theoretically chime in about this cool online thing they used in school that just plain works.)
Anyway, that promise is in writing on the website, and I get to field a dozen requests a day (and the subsequent stream of thank you mails that come back), but every once in a while somebody will write in asking for a free license to run their online tutoring business. I don't feel bad at all pointing those folks to our API page and explaining how they can get their site up and running as soon as they buy a subscription.
So no, if you give it to one person you don't have to give it to everybody else.
You can always use your judgement - there doesn't need to be a policy of giving your product away for free. If you detect that the requests have become too frequent or you start getting many similar requests, its easy to respond with a friendly email that doesn't give away your product.
