Search Engines: To Spam or Not to Spam?

Those who consiously take excessive measures to rank high in search engines are called SEARCH ENGINE SPAMMERS. Recognize and avoid the following illegal spamming techniques:

- Hidden and invisable text
This is defined as the use of text the same color as the background. The characters are not seen to the naked eye, but search engine spiders are able to match your font color with the background settings, or making the text invisible with the help of CSS.
- Excessive or irrelevant use of keywords, aka keyword stuffing (applied to any area of the HTML page).
- Redirects
On-page redirects with the help of the META refresh tag
- Pages or sites with duplicate or mirror content
- Link Farms
- Doorway pages
- Excessive website submissions
Search engines do not like being spammed by repeated submissions of the same page over and over again.
- Dynamic page generation and cloaking
- DHTML spamming
DHTML allows for the content to be visually spread into different layers, one above the other. Using layering, spammers hide layers of keywords beneath graphics.

You can access and read the Google's guidelines concerning unethical promotion techniques here: http://www.google.com/webmasters/guidelines.html

And, don't forget - Search Engine Programmers are aware of EVERY spamming technique nowadays existing.