I just finished my thesis on the topic. Check out #selfdrivingcars, which I've been populating over the last year. I find it very exciting - this is one of the things that will impact your life, and it will happen sooner than you think.
How long has this tech been around?
Depends on where you draw the line between 'robot 1970s Roomba finding its way around boxes' and Google's fully automated car.
Most people draw that line in 2007, when DARPA held a challenge to see who could build a self-driving vehicle. Every vehicle failed to go farther than a few miles before ending up in a ditch. DARPA decided to hold the contest again two more times, and by the third time it was good enough to merge into traffic and park itself. Google stepped in and employed most of the winning teams to work on their self-driving technology. They've been making the most progress, but there are car companies with similar aspirations and some isolated research projects working on getting this technology on the road.