I think you could make an argument that posting snippets directly from another article (especially giving the link back to the original) will fall under the fair use doctrine especially if you are using the cut/pasted info to comment on the article itself. However in the US its a very very very very grey area. Because it is so ill-defined copyright holders (or more probably their lawyers) take the view that fair-use doesn't exist at all.

That said, there hasn't been enough court cases to define the fair use to provide clear guidance other than what is written in this link by the US Copyright office.

http://www.copyright.gov/fls/fl102.html

I am an advocate of as little copyright as possible. (removed a long diatribe on why copyright is bad...)... rant over.