Boston IMC has a good story on the background of PepperBall technology. Of particular interest are the two fairly academic overviews of less-lethal-weaponry and it's application as a political deterrent that are linked at the end of the article.
But according to studies of some police departments, more than half of the people who end up on the business end of non-lethal weapons are not criminals, and over 80% are not threatening officers or the public with weapons of their own.
Non-Lethal Crowd Control Kills The Seattle Police Department announced they will stop using a particular piece of equipment referred to as non-lethal crowd control while investigations are pending into the death of a Boston Red Sox fan. According to a report released yesterday the officers in Boston who used the pepper pellet guns, killing one woman, were untrained in its proper usage.