Our cable provider has such an initiative. You can opt-in to open your internet connection (separate bandwidth of iirc 2Mbit and separate network) for other customers. You can only use it, when you share as well.
It is sometimes nice if a neighbor has it open and your own modem is not working properly. Also neat, I could use it in two countries so far (Poland & Switzerland)
The initial outcry of users was quite high, as of course nobody wanted to lose bandwidth and have other on "their" network.