It's much more unlikely that there is a sniffer between your ISP's routers and the target servers for interesting traffic than an attacker listening to your AP

It's much more unlikely that there is a sniffer between your ISP's routers and the target servers for interesting traffic than an attacker listening to your AP traffic. Your ISPs have a vested, primary business interest in keeping their network and peer traffic secure. The coffee shop could care less if people hack each other's Twitter over their AP. Think about it, say you want to grab somebody's credentials for a popular website. Do you a) hack into their ISP or b) follow them to a coffeeshop and open up Firesheep. What's the easiest angle you are going to take? Local network sniffing isn't the trivial example of sniffing, it's the most vulnerable and probably most exploited target. (Just ask Google.)