Just Ad-hocs? Um, no. (Score 1)

Um, this doesn't just apply to ad-hoc networks... Any monkey running linux with Hostapd can set up an full Access Point that your laptop will happily connect to even when ad-hoc networking is turned off. If this monkey is clever, he'll use the same open SSID the airport/coffee house/hotel is using. You can go on and on about SSL and vpns and so on, but the bottom line is the attacker has control of the WLAN you are connected to at the very lowest levels. The attacker has complete freedom to record and/or tamper with anything you send or receive while in transit.