http://www.google.com/support/...ers/bin/answer.py?answer=35769 
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Quality guidelines - basic principles
* Make pages for users, not for search engines. Don't deceive your users or present different content to search engines than you display to users, which is commonly referred to as "cloaking."
* Avoid tricks intended to improve search engine rankings. A good rule of thumb is whether you'd feel comfortable explaining what you've done to a website that competes with you. Another useful test is to ask, "Does this help my users? Would I do this if search engines didn't exist?"
* Don't participate in link schemes designed to increase your site's ranking or PageRank. In particular, avoid links to web spammers or "bad neighborhoods" on the web, as your own ranking may be affected adversely by those links.
* Don't use unauthorized computer programs to submit pages, check rankings, etc. Such programs consume computing resources and violate our Terms of Service. Google does not recommend the use of products such as WebPosition Gold™ that send automatic or programmatic queries to Google.
Quality guidelines - specific guidelines
* Avoid hidden text or hidden links.
* Don't employ cloaking or sneaky redirects.
* Don't send automated queries to Google.
* Don't load pages with irrelevant words.
* Don't create multiple pages, subdomains, or domains with substantially duplicate content.
* Don't create pages that install viruses, trojans, or other badware.
* Avoid "doorway" pages created just for search engines, or other "cookie cutter" approaches such as affiliate programs with little or no original content.
* If your site participates in an affiliate program, make sure that your site adds value. Provide unique and relevant content that gives users a reason to visit your site first.
If a site doesn't meet our quality guidelines, it may be blocked from the index. If you determine that your site doesn't meet these guidelines, you can modify your site so that it does and request reinclusion.
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