if you buy your polaroid film on ebay don't be too worried about the expiration date. i recently acquired some expired spectra film and learned that, while unpredictable, expired film can have a cool effect. below are some photos i took of one of my favorite models, paulette.
the greenish spills on the corners and the the yellow blob that looks like a thumb print on the bottom are unpredictable effects when taking a photo with expired film. you don't really know when it's going to appear and where on the image it'll manifest. but that's part of the fun. the dingy tint of the image makes it look like it's been sitting in an attic for years. also, look closely and you'll see a thick purple line going through the middle. i think it looks like the beam of an alien spaceship. especially in the second one, where it appears polly is being beamed up.