Fair Use, Copyright, and Risk

I am not a lawyer!
(I.e., this is not valid legal advice)

http://www.loc.gov/copyright/

The Library of Congress Fact Sheet (FL 102) on fair use states: "The distinction between 'fair use' and infringement may be unclear and not easily defined. There is no specific number of words, lines, or notes that may safely be taken without permission." According to Title 17, sec. 107 of the United States Code, the four elements to be considered in determining fair use are:

1. the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
2. the nature of the copyrighted work;
3. the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
4. the effect of the use upon the potential market for or value of the copyrighted work.

Since the wording in the United States Code on fair use is undeniably ambiguous, it is only through litigation that specific cases of copyright infringement are resolved. Anyone can claim the application of fair use, but whether such a claim is valid or not is only resolved by litigation from an aggrieved copyright holder. It is via the judiciary that the fair use provisions actually get weighed and applied. Inspection of such cases indicates that financial damage to the copyright holder is the most probable cause of litigation.

This leads to an interesting conclusion:

The application of fair use is related to the claimant's level of risk tolerance.

1. To what extent does a claim of fair use actually satisfy the ambiguous wording of the law?
2. What is the likelihood that the copyright holder will litigate?