Restrictions to copyright rights fall into 3 large categories:
Fair Use, which is the main constraint; First Sale, which carries certain rights for the purchaser; andlibrary preservation, by which libraries are granted certain rights to ensure the preservation of cultural material, including archival duplication etc.
We'll consider the first two as generally useful.
First Sale: The principle of First Sale is that you have the right to sell a book used. You didn't lease the information in the book, you bought it, and you can sell it or give it away at your discretion without informing the author. The pre-digital era assumption was that there was only one book and you sold it and it was gone, you didn't have it any more. In the digital domain, that's not really true. In fact it's very hard not to accidentally proliferate copies of works all over the place, let alone be certain that if you sell a digital artwork that you've transferred and not duplicated all of the relevant bits, especially since a move operation in a computer is a copy followed by a delete... At the moment you generally don't have the assumed right of first sale for digital works, but you still do for works fixed in/on some medium if that medium is what is transferred. Legislators get all fuzzy here, it's not the paper or plastic your selling, it's the data, but first sale applies to the artifact.
In my opinion, first sale clearly illustrates that data wants to be free.
FAIR USE Fair use is insanely complex so I'll just summarize: Criticism, comment, news reporting, teaching, scholarship or research is fair use when the relatively clear test is cleared that the use cannot reasonably be expected to result in lost sales for the author. If you're 2liveCrew you can parody pretty woman too.
Most fair use literature focuses on academic use, but most of us care about the 1984 Sony ruling which specifically allows you to time shift, or copy a TV broadcast onto a VCR and watch it later, and is generally construed as to allow you to tape, for personal use, your CDs and listen to them in the car where you, for example, don't have a CD player, and similiar activities which are for personal use.
Fair use is basically all fucked up by the WIPO compliance bills, and despite some improvements, is still insane. In general, in this room, its safe to say that most anything you want to do with data is not fair use and is probably a criminal copyright violation under WIPO and that includes activities specifically allowed by the Sony ruling.