You are meant to shave downwards as it stops any rashes because it doesn't irritate the skin, apparently!! I saw it on a show about porn stars shaving their pubic hair.
I have always shaved upwards-on my legs, as it just seems right, but I seem to get a rash now...don't have a clue why, but my dh has a new rasor that vibrates as you shave and I used this the last time I shaved my legs, and I didn't get a rash.