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I think the problem is that you can't say for sure if it's a penality or caused by something else.
Only Google knows that, there is a few things which you should stay away from if you don't want to risk a penalization, they are mentioned on the Google Webmaster pages (at google.com)
[webmasterworld.com...]
As lazerzubb said, no one but Google knows for sure what the penalties are and these may be different dependent on the circumstances.
The thread hanewich offered is a good one for sleuthing out the possibilities. Look to see if you've employed any of those on your site, look to see if you've employed two or more of them, then use the site search [searchengineworld.com] to read past threads about penalties. Try searching on PR0, google +penalty, duplicate (or mirror domains), read some of the "Google Update" threads.
After you read some of these threads you will see that many people have differing opinions so a check list might be misleading to some and "right on" for others.
Google Webmaster Guidelines [google.com]
- Start with google's general information for webmasters [google.com].
- Then read about the google guidelines [google.com].
- Also good to learn about penalties is reading google's seo info page [google.com].
I guess a list of possible penalties isn't necessary. Just allways think worst case - your site will get booted and kicked out of google if you don't follow their guidelines. It's just that simple to stay safe.
<added>what ... i typed 7 minutes!? phhh... </added>