My pal Simon Dumenco took on HuffingtonPost for its aggressive aggregation—paraphrasing his entire article with an unappealing, and demonstrably unsuccessful, link at the end—and won: HuffPo flatly accepted the criticism and suspended the writer behind the post.
It's an interesting topic. I do my best not to include too much and to try to drive people to the articles I'm aggregating, and of course I also do lots of 100% original stuff—"Guydar," play reviews, pop-culture essays. But it's a fine line, and many blogs get too far into it.
Other blogger friends know how great it feels to be linked by a major blog—and how disappointing when the link is small and the guts of your piece (or "your" piece if it's just a matter of you having found something of someone else's and blogged it "first") are entirely used up on the other site.