The offer of free stuff has coaxed me from lurker status..
the skulls are multipurpose, they show:
The joy of buying and using bbbastard bb's. (they're always smiling!)
The badass nature of bbbastard bb's. (skulls = death = awesome)
And simply because pirates are kickass. (widely known fact = good hook)
images are so large because they are the 8.8x8.8 at 300dpi requirement 