For Comcast, this is great: it lets them boast of having the largest network of public wireless hotspots in the United Stated. For its customers traveling around the country it is likewise great: they pay for service at home, and get free access to the Internet on the road without having to eat up their cellular data plans. There is an unintended side effect though.
When you connect to a wireless network, you typically create a "wireless profile" so your device will remember that network in the future. This means you only have to enter the network password one time, and your device will remember it for future use. Android and iOS devices automatically remember networks that you have joined; Windows will do this by default, but you can optionally uncheck the "Connect automatically" checkbox when initially joining the network. Whenever your device encounters a network that it has a saved profile for, it will automatically join that network. So what happens when your home router is broadcasting a signal for both your private network, and the xfinitiwifi public network?
Devices have different methods of choosing what network to join, but the most common is whichever network the device most recently used. This is true of most mobile devices, and as of Windows 8, Windows laptops as well (Microsoft provides some guidance on how Windows selects the network to join, but for Windows 8 it's essentially "prefer most recent.". Therein lies the unintended side effect: if you are a Comcast customer whose home router broadcasts the Comcast / Xfinity public hotspot, and you connected to another Xfinity hotspot away from home, guess which network your device will prefer when you return home?Think about the activities you do at home that you (hopefully) might not do on a public network - in particular online banking and private email. AARP surveyed residents of Washington state, finding that a quarter of adults connect to public WiFi at least once a week, and of those a quarter admit to doing personal banking from public networks. I would hazard a guess that many others didn't realize they were doing their banking from home, but on the public WiFi provided by their Comcast router.
What to do? Widely available public Internet is convenient. Silly lawsuits aside, what Comcast has done provides a legitimate benefit to their subscribers, as well as to non-customers that are willing to pay for temporary access. It does mean though that customers of that Internet provider need to pay attention to the network their mobile devices join at home, and if a device has joined the public hotspot from home, manually select the appropriate private network.