Anonymous Delivers.
Judging by signs like "Longcat is looooooooooong" and "Honk if you're driving a car", I think we can assume that the Anonymous protests were neither insidious nor angry-solemn. It looked like much fun. There were other "serious" signs, of course, but I like the fact that this ginormous group of people worldwide, with all their differences, got along well enough to both achieve their common goal and have a ball.
[Fun links]
Deathboy's livejournal post on the event in London
The /i/vasion - A snapshot of London
Metroblogging Los Angeles
For more information, there's always wikinews. :)