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The general rule of thumb most sites tend to follow, if they are not trying to rip others off, is to grab three or four lines of text, and include a link to the original page. That is clearly acceptable in most cases and according to most established norms.
Even then though, if the majority of one's content were still mainly snippets from other sites, I dunno how well that would go over with the SE's (never tried anything like that).
Basically, the SE's want to reward sites with lots of unique, original content, so if your site has a lot of that, in response to the articles you're linking to, then you'd be fine. If not, probably less than fine.
My 2 cents. :)