Among the many provocative answers to this year's Edge question, "What Will Change Everything?" my favorite was Sam Harris' "True Lie Detection":
The greatest transformation of our society will occur only once lie-detectors become both affordable and unobtrusive. Rather than spirit criminal defendants and hedge-fund managers off to the lab for a disconcerting hour of brain scanning, there may come a time when every courtroom or boardroom will have the requisite technology discretely concealed behind its wood paneling. Thereafter, civilized people would share a common presumption: that wherever important conversations are held, the truthfulness of all participants will be monitored. Of course, no technology is ever perfect. Once we have a proper lie-detector in hand, we will suffer the caprice of its positive and negative errors. … But some rate of error will, in the end, be judged acceptable.
I'm more skeptical about developing unobtrusive detectors soon, but even cheap obtrusive detector-caps would change a lot; by refusing to put one on you'd be admitting you expected to lie. Of course by asking someone to put one on, you'd be admitting you don't trust them, but such admissions are already pretty common today.
I'm also more skeptical that "lying" is such a clear categories of mind states. Many people seem to find it relatively easy to find a state of mind where they can "honestly" saying whatever is in their interest to say, no matter what other beliefs their minds may hold. A world of cheap "lie" detectors would reward people with good self-deception abilities, and encourage others to train such abilities. Perhaps we could also develop self-deception detectors, but I expect a murky mess of an arms race to follow. Still this is indeed one of the biggest changes likely to come in the next twenty years.