Two Answers for All Serious Free Software Contributors
"What do you think is the most important single-sentence of advice that you can offer to someone who wants to contribute to the free software community?"
He who does wins, so don't let the bastards grind you down.
"If you had the opportunity to say one sentence to someone who knows about computers and free software (EG they have used both Linux and Windows and done a small amount of programming) to convince them that they should join the free software team, what would it be?"
Imagine every bug you found could be fixed by you if you want, or a friend, or an enemy, or someone you hire, or the original developer, or whoever and that it's your choice who you ask to do it, with no veto from the copyright holder: that's free software.
The second sentence is a bit long, but I found it hard to encapsulate the power of that freedom in one. I use the bug example rather than costs or anything, because I think that's what will be most attractive to someone who has done a bit of programming: the right answer to "why can't I fix this trivial bug?"