Jon Pipitone, who was once a student of mine and is now a friend, volunteered with the Canadian Civil Liberties Association as an observer during G20 in Toronto. I know it's a cliché, but Jon really is one of the nicest people you'll ever meet, and one of the gentlest as well. Despite that, he spent almost 22 hours in lockup. He recently posted his account of what happened; knowing him as I do, I believe it to be accurate (if anything, understated). I am angry that the police stood by on Saturday and let people smash windows and burn cars, then turned around and arrested people like Jon. I'm even more angry that there will almost certainly never be a full accounting: we'll never know where a billion-plus dollars of public money went, how it was that legislation giving police extra powers was passed in secret, and---well, read Cllr Janet Davis's piece for the rest of the question (if you can get past the formatting glitches).
I'm very proud of Jon for getting out and doing something constructive; I think society would be a lot safer if more people followed his lead.