Anyway here is Google's thinking on what they termed duplicate content

Anyway here is Google's thinking on what they termed duplicate content. "Duplicate content are substantive blocks of contents within the same domain or across different domains that are identical or very similar". "Forums that generate both regular and stripped-down mobiletargeted pages, store items shown (and - worse yet - linked) via multiple distinct URLs, and so on. In some cases, content is duplicated across domains in an attempt to manipulate search engine rankings or garner more traffic via popular or long-tail queries". If you find someone else duplicate your contents, write to them politely and ask them to remove them.

If your contents are in multiple languages (for example English and Spanish) then Google doesn't view that as duplicate content. Occasional snippets such as quotes also won't be flagged as duplicate content.

What does Google do if it finds duplicate content? Google wants to filter duplicate contents from the search results as it wants to present a diverse cross-section of unique content in the search result.

"In the rare cases in which we perceive that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved.
However, we prefer to focus on filtering rather than ranking adjustments ... so in the vast majority of cases, the worst thing that'll befall webmasters is to see the "less desired" version of a page shown in our index".

All this while, people have been using Pay-Per-Clicks through Google's Adword and Adsense systems. These packages offer advertisers a means to bring in customers by paying a small sum of fee for each click, irrespective of whether the visitor buys or not. It has been very popular with new websites that has not gain any ground on the search results listings and it offers immediate visitors.

However, some people misused the system and tried to cheat advertisers by falsely clicking on the paid links. It is known as click fraud. They use people from third world countries to intentionally click on advertiser's paid links. The advertisers unknowingly pay for these clicks and the fraudsters collect part of the payment from Google and even split their ill gotten gains with the people who were lead to click the links. The search engines are concerned with these miss deeds.

In order to overcome this problem, Google came up with Pay-Per-Action where advertisers need only pay when the click leads to a buy. Fair game then, but it is still too early to know whether it will replace the problematic Pay-Par-Click system. This new method will however impact on existing affiliates programs from Commission Junction, Link Share and Click Bank as they operate a similar system.