I suggested earlier in the Quantal cycle emabling connectivity checking by default; the suggestion brought up quite a lot of interesting discussion which we should bring back at UDS.
There are some clear benefits such as being able to handle captive portals more gracefully, but there general idea of being able to know whether an "online" state means having actual Internet access or not brings some benefits, but introduces issues that we need to be prepared to tackle, such as how to reasonably know whether the Internet is reachable, what external servers to use, and how regular traffic generated from this would affect these servers.
What needs to be done for connectivity checking to be working properly and efficiently for everyone? How can we make sure privacy and other concerns are taken into account? How can we use connectivity checking to improve the user experience on Ubuntu? Where does connectivity checking tie in to Ubuntu on different form factors? Where could this fail horribly? How can we best test such a feature?