Good point.

But if there are a lot of laptop-using customers even a security camera shouldn't be too much of a problem. After all, just being there is not a crime in itself. And wiping your system will delete all evidence that could link you to any log files.

Or devise some system that can autonomously sniff from inside a laptop.

Even better, use a tiny embedded Linux device like gumstix (http://www.gumstix.com/). You could even hide it somewhere and leave, let it do it's thing, and either pick it up later, or have it transmit it's findings to you over the net (through some anonymous proxy, of course)

And this is why SSL is important.

Just don't go inside the coffee shop. Do it from a car or the restaurant next door, just to be safe.

Or better yet, drive down the road looking for a resident with an unprotected WiFi connection.