There is a bona fide scavenger hunt for Deus Ex: Human Revolution going on in the U.S. Download the iOS app (here), and start by scanning this QR code on Facebook or this one from the game's forums. After that, you can start hunting for QR codes in the real world and online. Hints will be given on Twitter and Facebook.
You can win some prizes: the first 1,000 people to find 10 codes win a theme, and the first 10 people to find all 21 QR codes win the Augmented Edition, custom DXHR headphones, Adam Jensen action figure, and a compression sleeve. But let's be honest, you're not going to go out and hunt for these things outdoors.
If people get a collective 1 million points before August 23rd though, all participants will get an exclusive Xbox Live Avatar prop (I hope it is a bomb) or PlayStation Home thing. So you might as well register, and let other people do the work for you if you are too lazy, a foreigner, or both -- like me. The app also gives you some wallpapers and lock screens, so it's not entirely useless if you are a fan of the game, but not a fan of scavenger hunts.
Ok, with that out of the way, here's the thing. I read "QR missions" as "VR missions" at first, and got excited about the prospect of Assassin's Creed: Brotherhood style VR missions for DXHR. Think of how much extra fun they could put into the game by releasing VR missions like that, without having to tie it to the story.
Not all of the AssBros missions were as fun to play competitively, but I can see something like that work for DXHR. Brief sneaking missions, assault/shooting missions, time-based objective missions, most melee kills in a row, etc. All as free DLC with leaderboards preferably, to keep people from returning it after finishing the game. Hell, I'd probably even pay a few MS Points for it if Tracer Tong gives you the mission objectives. You hear that Eidos Montreal? You'd be silly not to do it!
On a related note, community member Wry Guy will be recording a Deus Ex Nostaljourney podcast this week with a couple of community members, Jonathan Holmes, Tony Ponce, and myself. We'll be talking about why the PC version of Deus Ex is the single best game of all time and things like that. Keep an eye on his blog for when it's up.