One of the reasons Davos works is its isolation. It's not one of those places where people dash out to a taxi because they have other business commitments in town.
Most people fly into Zurich, but then there are a variety of choices.
If you are a plutocrat, Helilink provides one of the most spectacular helicopter rides of your life. It takes about 45 minutes from Zurich airport to a helipad overlooking the Davoser See, the lake in Davos. That takes two and a bit hours. A similar length trip is on the buses which the Forum organises for participants. One of the good things about the buses is that you meet lots of other participants on the way.