Small Device

Recently i bought an Raspberry Pi B and it was awesome. It was quite fast for such a device and that got me thinking about something.

What if someone bought alot of mini computers and placed them around free wifi areas and started using them (proxy or whatever)

Is there another small microprocessor WITH wifi which costs almost nothing? I know there is an Raspberry pi that is even tinyer but is doesnt support wifi or an ethernet connection.

Thanks