And apparently those who do pay attention are ill-informed. There's nothing to "crack" on a public wifi network. That said wifi traffic capture is not a weekend job. You either need lots of transceivers in lots of places or specialized equipment with specialized antennas or both. Most intrinsically valuable passwords that would traverse the wifi are protected by ssl, which is not trivial to break. 99.999% of the traffic on any public wifi is totally worthless which contributes a steganographic obfuscation.
If you're after website passwords, it would be trivial to pull all the POST and HTTP Basic auth requests out of a capture. As you say, SSL is a different animal, though, assuming people pay attention to the warnings their browser gives them.
I was at Sharkfest last year (conference for packet capture and analysis using Wireshark), a surprising amount of people logged in insecurely over the open network. Other than Blackhat/Defcon, I can't think of a worse place to put unencrypted passwords over the air!
(As an aside, if anyone here is in tech and happens to be going to Sharkfest this year, PM me. Awesome conference)