Sites that Excerpt: Legal?

Excerpts from the NYTimes like the one below from the article: Copyright Challenge for Sites That Excerpt, are coming under fire. It is true that most of the challenges are for much larger pieces of screen scraping and some that precede general release. But I have been asked for internal enterprise blogs, what exactly is the limit for a quoted excerpt? 50 words, 100 ... a thousand? Somewhere in there. The answer for the fair use question is ... whatever does not provoke a lawsuit. Inside an enterprise I was told to beware. Big entities can always be targets of lawsuits. Small bloggers LIKELY not. There seems to be no precise answer.

Later I found this excellent article in Plagiarism today that quotes a suggestion: Always include a link to original article, use less than 50% of the original article AND 100 worlds total or less in the quote... . I always do the first two but have violated the last rule of thumb.

" ... Generally, the excerpts have been considered legal, and for years they have been welcomed by major media companies, which were happy to receive links and pass-along traffic from the swarm of Web sites that regurgitate their news and information.

But some media executives are growing concerned that the increasingly popular curators of the Web that are taking large pieces of the original work — a practice sometimes called scraping — are shaving away potential readers and profiting from the content ... "