There is no such thing as a 10% rule
Just because it is on the internet does NOT mean you can use it however you want
There is a term called FAIR USE. It refers to the non-commercial use of someone else's material such as posting a portion of an article.
"The "fair use" exemption to (U.S.) copyright law was created to allow things such as commentary, parody, news reporting, research and education about copyrighted works without the permission of the author. That's vital so that copyright law doesn't block your freedom to express your own works -- only the ability to appropriate other people's. Intent, and damage to the commercial value of the work are important considerations. Are you reproducing an article from the New York Times because you needed to in order to criticise the quality of the New York Times, or because you couldn't find time to write your own story, or didn't want your readers to have to register at the New York Times web site? The first is probably fair use, the others probably aren't.
Fair use is generally a short excerpt and almost always attributed. (One should not use much more of the work than is needed to make the commentary.) It should not harm the commercial value of the work -- in the sense of people no longer needing to buy it (which is another reason why reproduction of the entire work is a problem.) Famously, copying just 300 words from Gerald Ford's 200,000 word memoir for a magazine article was ruled as not fair use, in spite of it being very newsworthy, because it was the most important 300 words -- why he pardoned Nixon. "
http://www.templetons.com/brad/copymyths.html
How much of an article that it is ok to post is actually in heavy dispute right now
Since many authors get paid per click, it is a courtesy to link to the original post and not include the entire article
