What happens when you win a game you already own?

You would be expected to remove your entries manually. Not doing so would result in a re-roll, unless the gifter is too lazy to check.

You remove your entry in the other giveaways. Staying in giveaways where you own the games is a breach of the sites' posted rules.

You give it to me

Assuming you're in multiple giveaways for the same game, the odds of you actually WINNING more than one of them in a very short amount of time are pretty much zero anyways.

But as the rules state you should remove them from your list as soon as possible.

Note that if you already own a game you can't add that game to the list anymore (once you sync of course)

I was in several Portal 2 giveaways. When Steam had Portal 2 on sale this week, I bought it and manually removed my entries using the search feature.

Be sure to enter only one game at a time.

Presumably if this happened, you apologise profusely, explain how it happened and the giveaway gets re-drawn.

Here's what you do. If you say, Win one of the first two.:

Click 'Manage' at the top of the site.

Click 'Entries'.

Click the Filter Pull down at the top right of the box and set it to 'Open'.

Click 'Remove Entry' from all of the other Deus Ex Giveaways.

There, you cannot win the other one/two now AND you get your points you spent back on them.

You die of cancer.

I think a bigger concern, with small giveaways with multiple copies offered, you could win the same game multiple times in the same giveaway, then I have no idea beyond re-rolling.

no, you would have to manually remove yourself from them.