minneapolis has "the light rail" running from downtown to more residential areas or other business sections of the city. I've only used it once, but it is FAN-TAS-TIC.
If only I didn't work outside of the city.. lol. I really should move to the suburbs closer to work.
Rail systems are perfect for city commuters, but you have to build them right. It would also be a great addition to the already prevalent "park and ride" bus systems we have running in just about every major city already. Houston, for example, really needs a high capacity park-and-ride rail coming in from the west headed downtown, right along I-10. Perhaps even only with one stop on each end.
If you implemented mass-transit park-and-ride to shuffle people into houston, and then had another "light rail" system similar to the one in minneapolis running around downtown, you could get rid of 30% of houston's rush hour traffic, and that's a VERY conservative estimate.
The problem is the cost in money and time to put the system together, plus restructuring downtown to accomadate a new traffic system.
Unfortunatly train travel does not make sense travelling between the destinations all around the country. As mentioned earlier, countries that are small in landmass can have rails running between all major cities and constantly run commuter trains between them, but here in the US, our rail systems are better used as they currently are, to shuffle mass amounts of goods around. We already have plenty of train tracks built for traveling around the country, but the cost in time and money to get from one destination to another is great enough that air travel or driving makes much more sense.