Flash mobs first started appearing in the Phillipines and were a device used by the theatre of liberation network. The country had come under such extreme law that public and private gatherings were severely punishable. Flash mobs allowed for a period of brief performance, the shouting of slogans and dispersal of the protestors before authorities could reach the scene. Now, flash mobs are used less for political aggression and more for mere performance. They range the gambit from dance parties to pillow fights to a popular flash mob scenario called "bang". This is the first "freeze" scenario that I've seen work so well.
If you're interested in more performance based mechanisms of protest, check out The Playful Revolution: Theatre and Liberation in Asia by Eugene Van Erven. Van Erven lived and studied with Safdar Hashmi, India's foremost performance based political protestor. After Hashmi's untimely and tragic death at the hands of his own government, Van Erven wrote this book and did extended research in the Phillipines, Indonesia, Pakistan, South Korea, Thailand and India. Flashmobs is where it's at, y'all. It's stopped elections. It's blocked parades and confused police. All you have to do is be specific. Text friends with time, place, what to wear/bring and what to do at the specified time. Tell them to text their friends. Tell them to tell their friends to text their friends and so on. Show up and you have a protest that was easy to create, maintain, plan, not get arrested at and most of all have a fun and invigorating experience.