The web's biggest legal impact on businesses has been on intellectual property; stealing it has become a crime of convenience, and its effect on the music business has--in regards to its ability to collect fees on its disseminated product--been catastrophic. (The major labels may, in fact, be earning more money, but they are also unwillingly giving out a lot of freebies.) The film industry has likewise been impacted. We have more movies grossing a billion dollars than ever before, but we also have an unprecedented degree of video piracy happening.
Images captured from the internet have made copyright violation of photography cheaper and easier to commit; it has also made finding examples of this easier than ever. Artists and photographers can use Google Image Search to see if their products are being used by anyone who hasn't paid to use them, provided the pirated images are on a website.
Plagiarism, the dirty little secret of an alarming number of writers, is easier than ever to detect and has ended many high-profile careers among journalists and novelists. Particularly erudite paragraphs can be Googled and literary thievery can be detected with ease. A lot of academic papers, copied and pasted from Wikipedia or other sources, are getting their writers exposed and expelled. Professors have access to software specifically tasked for finding this.
And within the legal profession, updated law books and publications have been a critical industry for centuries, entrenching a high degree of literacy within the legal profession's practitioners. Now, any clerk can just consult Westlaw, a legal search engine. More information than ever is suddenly in the hands of many less-sharp legal minds. The repercussions of this are still playing out in courtrooms everywhere.