All they would see would be each other's address and that they had more or less paid the same guy at the same time. They would have to verify it with me, what was going on, unless the guys knew each other's addresses and could connect the address personally to the "other" guy.
That's more than enough. Consider:
1) Some guy on the Internet owes me 2 Bitcoins for a Steam game. I give him my address. He knows my forum identity which leads him to my real name and address.
2) I sell my house for 15,000 Bitcoins. I give the buyer my address.
3) The guy on the Internet now knows I control 15,000 Bitcoins and he knows I haven't yet spent them. He has two tough guys show up at my real address with a wrench. Once they compel me to transfer the Bitcoins, chances of recovery are near zero. And I can't even really link the tough guys to the guy who bought the Steam game.
Re-use addresses at your own risk.
Yeah, this is a good example. Thanks.