A fun comic about seashells and Bayes' Theorem. http://xkcd.com/1236/
The formula he wrote is wrong, you'd need to switch P(I picked up a seashell) and P(I'm near the ocean) for it to be right.
I agree that the formula is wrong. I considered the possibility that it was sarcasm, but either way it's wrong.
A fun comic about seashells and Bayes' Theorem. http://xkcd.com/1236/