HPV isn't the only virus you can pick up at the spa. The H1N1 virus (more commonly -- and misleadingly -- known as the swine flu) makes an appearance as well.
H1N1 is a highly contagious strain of the flu virus. One big reason for this is that most people have no immunity to it, because it's new. It spreads just like the "regular" flu virus -- someone infected with it coughs, sneezes or touches their mouth and then makes contact with another person or a surface someone else will touch.
The virus can survive outside the body for up to eight hours, meaning that an infected customer at a salon can unknowingly booby-trap the establishment with the virus. With all the hand-to-hand contact that occurs in a salon, it's not difficult to understand why swine flu could easily spread between employees and customers.
So how can you avoid it? Ideally, salon workers wear protective disposable gloves for each client and change and gloves (with a hand washing for good measure) between appointments. All instruments should be treated with chemical germicides.
And if a salon employee is exhibiting flu symptoms, reschedule your appointment. Likewise, if you're infected with H1N1 (or show any flulike symptoms at all, even without diagnosis), cancel that appointment, no matter how much attention your nails need.