In the days leading up to Christmas, Steam is doing something crazy and proposing a treasure hunt on their storefront.  Details are in the link, but apparently every two days from now until December 20th, new objectives/achievements will be listed on Steam's page, varying from profile edits to actual in-game achievements.  Complete ten objectives by the end of the promotion, and you'll be entered for a chance to win 100 games of your choosing.  Complete one of the objectives every two days, and accordingly, you'll be entered for a chance to win five games from your wishlist.

And of course, most importantly, complete enough objectives and you'll win hats in Team Fortress 2.  Five objectives gets you a bounty hat, fifteen a Treasure hat, and ALL objectives gets you a Hat of Undeniable Wealth and Respect.

BRB guys, buying R.U.S.E., Chime, and Poker Night at the Inventory to get that last hat.