None that we have encountered. And we've done quite a few apps like this. I'd highly recommend ShrinkIt for shrinking the Illustrator exported PDFs, as it can

None that we have encountered. And we've done quite a few apps like this. I'd highly recommend ShrinkIt for shrinking the Illustrator exported PDFs, as it can reduce the size by as much as a factor of 10. Also PDFs really lend themselves to being dynamically tinted. You can use the new render mode in iOS 7+ or something like UIImage+Tint to make sure your key colours are all well defined in your code. (It's really nice when a client suddenly decides they want their app to be orange instead of blue, and it's a one-line change without touching a single asset.)