Daily Wireless suggests that Portland, Oregon's new I-5 corridor-paralleling light-rail line should have free Wi-Fi at each stop paid for by advertising: It's not a comprehensive plan, but Daily Wireless provides its two cents on how the free service could easily pay for itself, while enticing more riders to the new line. (The article is one of the reasons I'm making Daily Wireless a regular stop in my reading.)
This idea could be extended even further when PC cards and integrated wireless in laptops combine 2.5G, 3G, and Wi-Fi. Imagine arriving at the station, getting some work done on Wi-Fi, hopping on the train, continuing to work on Wi-Fi. As the train leaves the station, your PC card or laptop mini-PCI module switches automatically to the highest speed 2.5 or 3G signal you've paid for that's available. As you near the next station, Wi-Fi switches over again.
Or, Wi-Fi could be enabled the entire time in the train and stations, and the trains could switch backhaul from a local WiMax or Wi-Fi bridge while in stations to 2.5G/3G while en route.
Techniques like this could increase productivity and reduce the amount of wasted commute time that people have to make up in other parts of their days. I'm not suggesting that folks should stop reading books on trains. But rather if you can get an hour of work done in the morning and evening it just might cut up to two hours out of the rest of the work day. I know many of the ferry commuters in the Seattle area find this to be the case.