Our teaching pastor is also a lawyer so "Thou shalt not bear false witness" was interesting. Apparently in the judicial system of the time, if you accused someone and couldn't prove it to the satisfaction of the judges, they let him go and applied the punishment for his crime to you.
Taking the general principle of "don't lie", he cited a study done at University of Virginia in which people reported their conversations. If I recall the numbers correctly, the study found that people on average tell a significant lie in 30% of all one-on-one interactions, and 50% of conversations which last 10 minutes or longer. Men tend to lie to make themselves look better; women lie to make other people feel better; but they both prevaricate at about the same rate. The type of conversation which had the highest rate? College students talking to their mothers.