There's a newsy article written this week by the Swiss Info detailing much of what is open and what is still being re-routed to the flooded regions of Switzerland.
Much of the flooding occurred just 1 day after we departed Switzerland. The heavy rains occurred from August 19-22 which closed many tourist regions in Switzerland. The cantons of Bern and central Switzerland were the worst hit. Such areas using the scenic rail to Montreux will have to take a bus in areas of Zweisimmen and Wimmis.
Lucern and central switzerland are the most affected so make sure you read the article if you are wondering about the Lucern or Bern floods. I'd imagine the floods from hurrican Katrina are much worse. Some areas are at least 10 feet below sea level. Talk about damage to deal with. I'm sure Switzerland is now thankful they were not hit as hard as the US.