My colleague Ilya Somin writes at the SCOTUSblog:

Justice Thomas' dissent does an excellent job showing that the original meaning of "public use" was either actual public ownership of the condemned property or at the very least a legal right of access by the public (as in the case of takings for railroads and other common carriers). It did not mean a mere potential benefit to the public, which is why the text does not use a term such as "public purpose," which the Kelo majority uses interchangeably with "public use." Many state supreme court decisions explicitly distinguish between "public use" and "public purpose" (I can provide cites to anyone who may be interested), and the US Supreme Court should follow their lead.

The majority cites late nineteenth and early 20th century Supreme Court decisions that seem to suggest that "public use" and "public purpose" or "benefit" are synonymous. However, not only are these statements mostly mere dicta (as Thomas points out), but the decisions in question are not even about the Takings Clause at all. As my colleague David Bernstein (a leading expert on the Lochner era) has argued [on a law professors' discussion list-ed.], these cases were in fact decisions about the limits imposed on eminent domain under the Lochner-era substantive due process doctrine protecting economic liberties through the Due Process Clause of the Fourteenth Amendment. Whatever one's views on Lochner, I think it's clear that Lochner-era "substantive due process" decisions are not a reliable guide to the meaning of the Takings Clause.