Frederic sent me this link, wherein an American DJ describes what happened at a big event where he was booked to play. The story starts as follows:

At about 11:30 or so, I was standing behind the stage talking with someone when I noticed a helicopter pulling over one of the mountain tops. I jokingly said "Oh look, here comes big brother" to the person I was with. I wasn't far off.

The helicopter dipped lower and lower and started shining its lights on the crowd. I was kind of in awe and just sat and watched this thing circle us for a minute. As I looked back towards the crowd I saw a guy dressed in camoflauge walking by, toting an assault rifle. At this point, everyone was fully aware of what was going on . A few "troops" rushed the stage and cut the sound off and started yelling that everyone "get the fuck out of here or go to jail". This is where it got really sticky.

To finish this off, check out this film taken from the stage, which shows police coming in by helicopter, threatening the people on stage, touting automatic rifles that they point at people, several police, armed to the teeth and protected with everything from vests to helmets, beating and kicking one person who is lying on the ground.

As the person with the signature mayhem puts it at the above linked-to forum:

America is headed in a very dark direction. This is just a preview of what's to come. In the following years the majority of simple freedoms we have will be taken away, with out any media coverage or high court to protect us.

Read eye-witness accounts of the event at this site.