I've been playing with it. I downloaded a few Polaroid actions to see what people were doing, then decided to go on my own.
A later attempt that I like better....
What I did today...
To make your own Polaroid, without any actions, in Photoshop....
make a new document that is 3.5 by 4.25 inches with a transparent background.
Select an area that is about 3.1 inches square.
Invert the selection.
Fill the selected area with whatever color you want your frame to be.
Paste your cropped and processed image in, put it behind the frame layer.
Then add type, effects or distress the frame as you like.
That's how I did it. But there are a hundred different ways to do any given thing in Photoshop. And there are like a hundred and one free actions out there that do this for you. Feel free to speak up in the comments with your method or a link to a good one.