Nanotechnology has been a fascination of mine since 1986 when I first read K. Eric Drexler's wonderful book Engines of Creation. If you haven't read it, I highly recommend that you do. It's a wild ride through our probable future.
Anyhow, I was particularly struck by one of the paragraphs in the wikipedia article that alludes to the class of bugs that all of us as programmers strive to avoid:
In a History Channel broadcast, grey goo is referred to in a futuristic doomsday scenario: “In a common practice, billions of nanobots are released to clean up an oil spill off the coast of Louisiana. However, due to a programming error, the nanobots devour all carbon based objects, instead of just the hydrocarbons of the oil. The nanobots destroy everything, all the while, replicating themselves. Within days, the planet is turned to dust.”
Let's not do that.