International Journal of Internet Research Ethics
(dedicated specifically to cross-disciplinary, cross-cultural research on Internet Research Ethics)
http://www.uwm.edu/Dept/SOIS/cipr/ijire/

Fair use.
Fair use is one of the most important, and least clear cut, limits to copyright. It permits some use of others’ works even without approval. But when? Words like “fair” or “reasonable” cannot be precisely defined, but here are a few benchmarks.

Uses that advance public interests such as criticism, education or scholarship are favored — particularly if little of another’s work is copied. Uses that generate income or interfere with a copyright owner’s income are not. Fairness also means crediting original artists or authors. (A teacher who copied, without credit, much of another’s course materials was found to infringe.)

Commercial uses of another’s work are also disfavored. For example, anyone who uses, without explicit permission, others’ work to suggest that they endorse some commercial product is asking for trouble! Yet, not all commercial uses are forbidden. Most magazines and newspapers are operated for profit; that they are not automatically precluded from fair use has been made clear by the U.S. Supreme Court.

Source: http://www.piercelaw.edu/tfield/copynet.htm