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Question: How does it, if at all, effect link popularity and positioning on SERP's?
you are talking about scrapper sites. these sites are auto generated. search engine results for targetted keywords are scrapped and the serp's sites are linked to automatically to create keyword specific content.you may sometimes see a thumbnail of your site next to your link too :)
This has been rampantly done lately and the scrapping is usually done from diffrent IPs and difficult to block