Here is a good question to ask if your website is being penalized by Google. How do you find out?. What are the signs or indicators to look for?. If you like to know more, there is a Google Group that focuses on these questions.
Some of the answers provided are like :
- Basically search under your domain name - if you aren’t listed and previously were than that is a good clue of a penalty.
- A sudden drop in traffic, while useful often leads to other reasons being discovered, but is surely a good sign that something may be penalized.
- If aboutus.org outranks you for your domain name, you’ve got problems and it probably has something to do with links, how you manipulated them, got them, or distributed them.
If you would like to know more whether your website is being penalized by Google, it is always advisable to check closely error reports reported by Google Webmaster Tools.