The ICE makes it from Munich to Frankfurt, for example, in just over three and one-half hours, and once a new high speed track is completed the trip from Frankfurt to Cologne will be less than an hour. You aren't likely to do better than that flying when you consider the time it takes to get to and from the airports. Also, flying is expensive and much more subject to weather-related delays. Because of this, major efforts are being made to integrate air and rail travel. The Frankfurt airport terminal is now open, and the one at Cologne is slated for opening in 2001.
Rail is often faster than driving, too, and much more relaxing.
On the trains you can do some work, read the paper, snooze or enjoy a sandwich and beer. And downtown parking is no problem. Major improvements are being made at the Bahn's main stations. The huge one in Leipzig, for example, has just undergone a two-year overhaul and is now a city center unto itself similar to Berlin's Euro Center. A century of expedient alterations has been swept away at the Frankfurt station, restoring its Victorian grandeur and making way for a new passenger center.