Short answer: Yes, both today and historically, especially when we meted out more brutal punishments. Literature on the history of jury nullification invariably points this out.
However, juror leniency has waned as jury pools have become increasingly composed of people who don't live in the same neighborhoods or socio-economic conditions as the defendants and therefore lack a more realistic perspective of the risks and benefits of leniency rather than being driven by fear. See, generally, The Collapse of American Criminal Justice by William Stuntz.