Should I wait for the key?

Giver has seven days to provide you with the game. I saw it rarely, but some prefer to wait that long for some reason, even if they could send the key otherwise.
Many people prefer to send the code or link in email: check your spam folder.
Others prefer to contact you in Steam chat. Make sure you remember the Steam name of the GA creator so if they add you, you don't ignore them.

Plus points for actually waiting over a day with this question though. My record was a winner asking for a key in 15-20-ish minutes after the GA ended.

The giveaway creator has a 7 day period to get you the gift.
Please be patient. People can get quite busy. :)
It's the giveaway creator's responsibility to get you the gift, so try not to invade their space by adding them on Steam.
Add a comment to the giveaway if you feel impatient.

Edit: Too late. :)

The giveaway owner has not been online for the last 4 days and the giveaway ended 2 days ago.

The owner has 7 days, only 2 have passed. You can let a few more days pass and see if he remembers it.

After the 7 days, you can try to add him on Steam to remind him of the giveaway.

Wait 7 days, if you haven't received anything comment on the giveaway or add the giveaway creator on steam. Wait for some time. Still no response? Mark not received.

Yup, you gotta wait. The person who set up the giveaway has to actually hit a "Send" button for the key to become visible to you, and yep, there is the possibility that they'll be sending it to you as a link via mail or an inventory gift via Steam. So just sit tight! :)

Wow. Thanks a lot.
Fastest answer ever! =)