Pamela Samuelson and Krzysztof Bebenek have self-archived "Why Plaintiffs Should Have to Prove Irreparable Harm in Copyright Preliminary Injunction Cases" in SSRN.
Here's an excerpt:
It has become lamentably common for courts to issue preliminary injunctions in copyright cases once rights holders have shown a reasonable likelihood of success on the merits without going on to require them to prove that they will suffer irreparable harm unless the injunction issues. Harm is too often presumed to be irreparable if plaintiffs have made out a prima facie case of infringement. This presumption cannot be squared with traditional principles of equity, as interpreted in numerous Supreme Court decisions, particularly eBay, Inc. v. MercExchange LLC, 547 U.S. 388 (2006).
While a presumption of irreparable harm is inappropriate in all copyright cases, it is particularly troublesome in cases involving transformative uses of existing works, such as parodies and remixes and mashups, because free expression and free speech interests of creative users are at stake and transformative uses cases often raise plausible non-infringement defenses. Indeed, if any presumption about harm is appropriate in transformative use cases, it should probably run in favor of irreparability of harm to the defendants' free expression and speech interests under First Amendment case law which treats preliminary injunctions as presumptively unconstitutional prior restraints on speech.