Oh yeah, there is a public Comcast hotspot on my block (I'm unsure if it was setup/operates standalone by Comcast or if it's a "guest" account from a Comcast customer's router). I did see a truck attaching something to a utility area (small power transformer + light post) before it went live. I will reach out to friends (a friend in NH has a 100mbit account with them... unsure about upstream, I want to say 30mbit, but I don't know if that even matters in this case because if are enrolled in their 25mbit tier or higher then you qualify for WiFi access) and test it locally. If it works I'll shoot you a PM.
Updated info:
http://wifi.xfinity.com/ - it seems like it's a mix of dedicated hosts and home users that make up the guest network. I assume speeds vary but if you have access to a xfinitywifi AP (shown below) then you should be good to go (an external antenna would improve the dB level).
