The truth is this, the issue of similar content affecting search engine positions has been overrated. Many sites still rank on the top for highly-competitive keywords although they have lots of duplicate content. The reason why many sites with similar content appear to get banned is because these websites may also contain other "black hat" tricks in an attempt to fool the search engines. The duplicate content thing is not the main problem. If you use content which is similar but stick to search engine rules and don't use black hat tricks, your site will be hard-pressed to be penalized by the search engines.
I have seen some strange things with duplicate content. I have seen the same page added into 2 sites on the same day and then only one of the pages comes up in the search results. There is nothing to do with domain age, links etc as the same thing was done on other occassions and guess what the site in the results changed to the other site as it must of been crawled first.
But how will google identify if someone publishes some post in a blog and that time only (after 10-15 minutes) someone copies the same content into his blog... in this way blog with duplicate content may also get benefitted. --Thanks...