Government already had the power to take private land for public use such as the airport runway or highway you mention. What this Court decision did was to expand the scope of eminate domain to mean that private land could be taken from one party and used by another private party for the "public good", i.e. job creation and increased tax revenue.
A developer in my town has been trying to buy the local Dairy Queen property because it borders an amusement park he is building. The owners, realizing that an amusement park will be good for their business, will not sell. With this Court decision, the delevoper can now argue that he has a legal right to the property because he will employ more people and pay higher wages, making it in the best interests of our community. As screwed up as our local government is, he'll win too.
Curt