The passengers on the morning commuter train from San Francisco to Silicon Valley, who look young enough to be carded at happy hour, are clad in shin-length, hip-hugging jeans and trendy pleather jackets, bopping their bleached-blond heads in time with the music from their CDman players. Although they may excel at office foosball and be handy users of PlayStation, the new economy's supposedly new breed of workers is not all fun and games. I count 12 people in my car punching away at their laptops and five others on cell phones arguing over cost reductions and ordering accountants to redo configurations. Caltrain officials say that more and more of these commuters are returning as late as the 9:00, 10:00 and 11:00 p.m. trains.