Update (5 p.m. EDT): The rally and concert at Union Square has attracted a crowd of thousands, with more acts on the way. New School Free Press editor Andrea Vocos tweeted this fun picture of Rage Against The Machine's Tom Morello leading a sing-along of This Land Is Our Land:

@NSFreePress Tom Morello's last words after performing "This Land is Your Land" = "take it easy, but take it" #ows twitter.com/AndreaMocos/st… — Andrea Vocos (@AndreaMocos) May 1, 2012

Update (4:35 p.m. EDT): The East Bay Express got a photo of that roughed-up CBS 5 news van in Oakland. Not cool, van-smashers!

Update (4:29 p.m. EDT): In New York, there have been a total of about 30 arrests so far, according to Yetta Kurland, of the National Lawyers Guild, which is handling legal defense for May Day protesters.

Update (4:23 p.m. EDT): KCBS reporter Doug Sovern reports some less-than-peaceful protesters stripped the CBS 5 news truck. If anybody has pictures, please send them:

Protesters in Oakland have attacked & "dismantled" a news truck from our TV station CBS5. Crew OK but truck stripped! #M1GS #Occupy #OO — Doug Sovern (@SovernNation) May 1, 2012

Update (4:16 p.m. EDT): Union Square from another angle, via Instagram user mostrower:

Update (4:10 p.m. EDT): It's time to change the lead photo, but this one from the Associated Press, of a police lieutenant swinging his baton at a masked protester during the wildcat march, is so dramatic we want to keep it in the post:

Update (4:08 p.m. EDT): In Oakland, things have calmed down a little, with protesters "slowly leaving the street" according to North Oakland Now. KQED, the local public radio station, tweets this photo of a police line holding at Broadway and 15th Street:

Update (3:59 p.m. EDT): On Twitter, photographer Katie Moore shares this shot of the crowd. Guessing that's about a thousand people. Maybe more. It's hard to see behind the trees.

Update (3:47 p.m. EDT): The rally in Union Square is pretty much in full swing, and reportedly peaceful. Instagram user verbosecoma captured this admittedly pretty cute nod to an icon of peaceful protest:

Update (3:33 p.m. EDT): Meanwhile, in Oakland, things have reportedly gotten a little out of control as police fired tear gas at a crowd on Broadway and 14th Street, according to the East Bay Express on Twitter. The crowd looks fairly calm on the Oakland Tribune's live stream, but an announcer can be heard in the background saying "the rally has been postponed due to cloudy weather with a 100 percent chance of tear gas). Activist Anthony Vincent tweeted this photo of a protester he said was injured by police:

Update (3:19 p.m. EDT): Most of the marchers from Bryant Park have made it to Union Square, but the march from Washington Square Park is running into conflict with police. Veteran New York reporter Harry Siegel tweets a report of arrests at 6th Avenue and Waverly, one of which apparently landed a protester a bloody nose. Instagram user christrobbins shared this photo: