I received a PDF by e-mail which is unreadable on my Mac (Lion 10.7.3) and on my iPhone (iOS 5.1.1) but the same PDF renders perfectly on Windows. If I use Chrome on my Mac, (which has its own built in PDF renderer and doesn't use the OS X one), it renders correctly as well. So far it's the only PDF I've ever encountered with the problem, but others are having similar problems.
I've attached a screenshot of the rendering problem, which is best described as rendering most text as a series of grayscale stepped gradients. Note that the grayscale 'bars' don't correspond directly to the missing lines of text. There's much more text than that.
Anyone have any ideas?