I've won several things through the old giveaways (thanks to mousers happiness calculator). I would fully support this idea as, like you said, only supporting members would be eligible and less likely to up and leave the site because they were only after a free product.
This suggestion is open, not to put a limit on who, or what, but to get an idea of what the community wants. I personally don't think that these should be open to people, who have obviously signed up purely for this reason, and will leave once they win or lose.
I don't disagree, that some will stay, but those people will be 1/100, and those numbers, hardly seem worth it.
We could limit to:
- Supporting Members
- Charter Members
- 25+ Posts
- Contributing Developers
- Contributing Beta Testers
- + More
The only real suggestion I have, is a total lockdown on people, whose FIRST post, is in a giveaway thread, and/or you can see their signup date corresponds to such.