Student physicists from the University of Leicester have theoretically proven that spider webs, if scaled up in size, could have in fact stopped a runaway train as scene in Spider-Man 2 (see video below to refresh memory).
From the Canadian Broadcasting Corporation:
The students determined that a real spider’s web would, in a proportional scenario, be strong enough to stop four New York subway cars packed with passengers.
Taking the conditions into account, they calculated the time and force needed to slow the momentum of a train heading at full speed if a series of webs were attached to the vehicle.
Um, yay?