Augmented reality is here now, and is going to get bigger fast. In fact, it's going to be a killer app for the semantic web.
Where did I come up with that?
Well, as far as not seeing it ... that's because it doesn't look like the picture you have in your head. You're thinking of stuff floating in midair like in Minority Report or at least a heads-up display with goggles or a sceen that overlays data onto video.
Those may be nice implementations. But the core utility of augmented reality is getting information on stuff you're near (where near can be physical or by mental association) and having it delivered to you in an actionable "heads-up way" even if it's not on a HUD.
In the information sense, AR is already popular. Joe calls Fred on his cell phone: "I'm trying to find a hardware store down here near 20th, can you hop on Google maps and find it?" Fred looks it up, maybe hits Street Views, done. Later he calls Fred again from a party: "That girl is here -- the one I met at your office party, used to work with you... what is her name? She's looking great. What is her whole deal again?" That's augmented reality by cellphone and human reverse TTY, call it v 0.5.
Then there's v 0.6, which is Google Local for Mobile/iPhone, Windows Live Mobile, or the like. GLM offers "My Location"-biased search results, while WLM has solid speech recognition (you can just tell it where you are or what you want). These mobile search products are great, except that they are relatively active, not passive -- you need to tell them what you're interested in, they doesn't already know. And they only knows a little bit about places and a little more about businesses.
Despite the limitations, these two methods are real examples of AR in use today, even if people don't call it that.
I assert that AR is a killer semantic web app because it's the semantic tools that let the machine filter the Internet down to what's relevant in your (metaphorical) field of view, when you're out in the real world.
Googling for answers in many real-world situations is drinking from a firehose, and you need to go all the way into the cyber world (iPhone, laptop, etc.) and invest effort to get what you want. That's not AR, it's just context switching and portable cyberspace.
AR is a system that can matrix your interests, contacts, places, and needs against all the current information germane to where you are or what you're doing ... and then pick out just the high level parts you want, with a mechanism to drill down by concept. Doing that by brute-force search, or even collaborative methods (think geotags), won't get you far enough. You need a true semantic layer to front-load the work and make this real-time.
On the other side, once you have a workable if basic semantic layer, then AR becomes a very basic incredibly useful flavor of personal, semantic search.