I was in a "webinar" (live online presentation thingy) recently with Erica Chenoweth from Wesleyan University. She was discussing her statistical work tracking contemporary nonviolent campaigns. Her data backs up what nonviolent strategists already know: it's better than violence and more effective.
One factoid I found particularly interesting: "Foreign states are more likely to support violent campaigns against their common enemies than nonviolent campaigns. This can increase violent campaigns success to 41%, but is still less successful than nonviolent campaigns. But nonviolent campaigns seem to be better off without foreign support."
Why Civil Resistance Works: The Strategic Logic of Nonviolent Conflict, by Maria J. Stephan and Erica Chenoweth
From 2000 to 2006 organized civilian populations successfully employed nonviolent methods including boycotts, strikes, protests, and organized noncooperation to challenge entrenched power and exact political concessions in Serbia (2000), Madagascar (2002), Georgia (2003) and Ukraine (2004