Nanobots are now a near-term reality. From ExtremeTech’s “Top 10 Tech Breakthroughs of 2011“:

“Nanorobotics 

One of the most marked breakthroughs in 2011 was our control of nanorobotics, or nanobots. We now have the ability to control nanobots inside a living, breathing body, and using them to deliver highly-targeted medications — like cancer drugs — is now just a year or two away.

When you factor in autonomous ‘Constructicon’ robots and this year’s discovery of one-molecule electric motors and ‘nanocars,’ it’s also humbling to think how close we are to a reality with swarms of nanobots that fly or float around building and maintaining our towns and cities.”