We had just opened our laptop this evening on our ride back across the Bay when a dialog popped up: "None of your usual wireless networks could be found. Do you want to join wifi_rail?"

Yes, please!

Looks like BART is test-running a free wireless network. Our laptop only picked up on it in the Civic Center-Embarcadero range (the same area where our cell phone works), and it didn't allow us to connect to the great wide Interweb, but we were able to register before the Transbay Tube shut us down.