What changed is that before, governments (City, State, Federal) could take land only for civil uses...a highway, police station, etc. After this ruling, they can take land and give it to private citizens that can use the land for private business that would provide more tax revenue.
2. This happened a couple years ago in my city as well. The city had lined up a large development to revitalize the west side. They offered many homeowner's fair compensation, and many took it, but a handful refused. The city decided to take the homes via eminent domain, citing the homes as being 'blighted'. The people fought back, started a petition and got a referendum on the ballot, and the business complex was voted down.
The thing about this whole affair that really set the city on fire was the city definition of blighted. By the laws of the city, 90% of the cities homes are blighted. The (ex-)mayor's own home is blighted. I don't remember everything about the laws, but the one I do remember, is that if your home doesn't have an attached garage, its blight.
3. A small town in Vermont or Montana or some other low population state has already acted on this new ruling. In their town is the estate of one of the supreme court justices that ruled in favor. They want to claim his land and turn it into a combination hotel/museum. The museum would be "The Museum of Lost Liberties".
4. Using this ruling, I want to see a group get together and try to get control of the Kennedy Compound. I would laugh my butt off at that.