Nothing to hide??
Every time I hear that phrase, I really want to slap whoever said it!
Someone bringing in a computer to one of these places is not an experienced user, so they are not going to have their private files on a thumb drive or encrypted. Its a miracle if everything isn't in the root of the C:\ drive most times. They will also have the passwords to every site they have subscribed to, including Ebay, Amazon, Pay pal, their bank, their kid's photos, their private adult photos of each other<who has a digital camera and never took a nude pic of themselves or their partner?>. People have got fired for less than this when such a photo gets discovered on the net.
There is no expressed or implied permission to root around someone else's computer at any time. No more than leaving your front door unlocked makes you responsible for being burgled, and vindicates the person who just walked in and started helping themselves to your belongings.
Same applies to someone who gains unlawful access to a network or a wireless node. Not securing it is not the same as allowing free use of the resource.
Happily, I'm never going to have to use such a place, and my friends all know better than to trust their privacy to some pimply kid in a computer shop.