i have to say i agree with qbtacoma...
unpaid internships are for the dogs. they have replaced entry level positions thus putting all those who come out of grad school looking for a place to get our foot in the door at a disadvantage.
you probably won't get the experience you want (i've done a couple of them - prestigious ones too - and you tend to just sit in the corner... or bring things to the post office) because as qbtacoma pointed out, they aren't going to give anyone unpaid real responsibility.
if they do by chance give you real responsibility, that's pretty much illegal.... and it's not very fair to be doing something for free that other people get paid to do.
i went to grad school in nyc and i hoped to find a job in art pr as well -- not a chance. but i was coming out of grad school in '08 so there were no jobs.
when i have kids i am going to warn them away from unpaid internships.