Legalities aside, Arrington seems to be facing a public relations crisis of sorts. But it doesn't stem from the fact that he disclosed Twitter's information, but that he told everyone that he obtained it from a hacker.
Had he simply written that the site had come into possession of documents showing details of acquisition talks, no one would think twice. Every day journalists publish information that's leaked to the press against a company's wishes. The difference is, most journalists don't also say how they obtained that information.
What's more, had Arrington kept quiet about his source, Twitter would have had a hard time forcing him to reveal it. California has one of the strongest reporter shield laws in the country. That law provides that journalists can't be held in contempt for refusing to disclose their sources. A state appellate court has already ruled that the shield law applies to bloggers. In that case, Apple unsuccessfully attempted to discover the identities of people who leaked information about the new product "Asteroid" to some blogs.
TechCrunch, for its part, is continuing to post the documents. A recent entry provides some details about strategies for dealing with Facebook and Google, goals for growth, and potential revenue models.
The lesson from all this outrage directed at TechCrunch seems to be that news is like sausage: People want the final product, but don't want to know how it's made.