I have made a new site where I post original articles but some of my users are posting articles from other sites, Should I delete them ? how does it affect ?
You will get penalized for duplicate content even if for the first time there will be positive results of this technique.
Many sites to copy others. And Google will soon do something on it. So let's wait. If your site has been copied or someone is using the same text as you do, you can sue the site provided that you already have "Copyright" on your website.
Any page that in orginal and unique will rank well with Google. But if the content has been copied from some where else and posted, Google will graybar the page which makes is worthless from a SEO standpoint. Note, any link from that graybar page will also be ignored.
Yeah you should delete them and keep yourself away from the google's policy of punishing duplicate content websites and blogs.
This seems to be true but how do article directory links work in that case. I have seen same article being indexed in multiple, in fact hundreds of sites and same press release indexed on thousands of sites. Also, I have seen many examples when Google shows links from same article from two different sites as link for that site when searched for (link:site.com). Is that because all the links point to the same source. If this was not the case the mass directory submission services will become redundant. I somehow am not able to find a logical reason behind this anomaly. I always have a debate about original content and I strongly believe that Google does have a system to check and penalize duplicate content but never able to understand how. Lets take an example: I have a site and I post an original article on it. Someone copies it from my site and posts it on his/her blog or site. Now if that page from site which was copied from mine gets indexed first, will it be deemed as original? These are some questions that I am sure Google engineers dont have an answer for and this is probably why they are not too harsh on the issue of copied content.