Eminent domain expanded

The US Supreme Court ruled 5-4 that government entities can use the eminent domain clause of the fifth amendment to seize privately-owned land with just compensation for the development of private enterprises, if it benefits the public. However, how do we define a public use? When does an enterprise benefit the public as much as the private entity?

Milwaukee Journal-Sentinel article: A looser rein on eminent domain

Chicago Tribune article: Eminent domain expanded

Fifth amendment, US Constitution