* Manual penalties are usually related to off-site over-optimization, i.e. forceful link building campaigns
    * Algorithmic filtering usually takes place with on-site over-optimization.
    * A manual penalty might only be removed in slow steps.
    * An algorithmic penalty is often removed automatically; it can also be removed with no apparent reason

Remember this too. If your competitor complaints you on your bad things, you will undergo manual review.

How to avoid Google penalty?

1. Make sure that your website is not linked to any spam websites, gambling & adult websites, banned websites and unrelated websites.

2. You check your server IP whether it has been blacklisted or not. If it is and cannot remove, change your server.

3. Don’t over stuff your keywords in content and Meta tags. Use only wherever it needs.

4. Don’t give excessive interlinks to the pages present in the same website. Extensive interlinking of all your websites, particularly if they are on the same C Class IP address will affect all your websites.

5. Avoid hidden text or links

6. You should not participate in any link farm. If you are interested in generating revenue through advertisement just go ahead by implementing no follow attribute for that link.

7. Excessive reciprocal link exchange will put you in trouble. It should be done only if they are relevant and useful.

8. Get one way links for your website slowly. Use different keywords for anchor text, don’t use the same for all back links

If you are sure that you haven’t done any violation of Google guidelines, request Google for reconsideration of your site – Check this link for more details.

http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=35843

The main penalties applies by Google are Minus 30 Penalty, Minus 60 Penalty, Minus 950 Penalty

The -30 filter is a penalty that Google applies to web sites that fail to use effective SEO techniques. If Google applies -30 penalty to a web site, the rankings of that site are lowered by 30 positions.

The -60 filter is a penalty that Google applies to web sites that use spam SEO techniques. If Google applies -60 penalty to a web site, the rankings of that site are lowered by 60 positions.

Websites that were ranking well can unexpectedly find that some pages or even the entire website now are listed on the end page of Google results. This loss of approximately 950 places is known as 950 penalty by Google.