What do you think is fair?

100 rep sounds cool.

I'm all for 705 rep. Maybe 706, but only from tomorrow.

3000

Up to the giveaway-er.

Whatever the person doing the giveaway thinks is fair. After all, they're the ones giving away the game(s). Their giveaway, their rules.

Random.org' it everytime.

100. BUT people who make giveaways should make exceptions for newer users for whom an older, trustworthy member has vouched for. Whom the gifters consider trustworthy or not is strictly their business.

I don't see any reason to tell others how to run their own giveaways. As far as I know, the only official rep requirement applied only to the steamgifts group.

Over 9000!

ninja giveaways: 100 rep + first person who PMs would be fair IMHO
contests: up to person making that contest

100 rep as a minimum is a great suggestion to people, it's up to them to accept it or not.

I think 100+ and first to PM is a good general rule.

I agree with 3000, but Portugal based players can't enter.

This.