Yes; Wireshark can be used to sniff wireless traffic (see the WLAN Capture Setup article on the Wireshark wiki).
Though, you will probably have better luck with Firesheep than Wireshark for what you want to do. Bear in mind, doing this in an Internet café is very probably a bad idea, against their specific terms of service, possibly illegal, etc. You shouldn't really be trying to snoop on other people's traffic.
answered 15 Feb '12, 07:55