Hey Mof3kz,
In my experience, a sudden drop like this is most likely an indication of a content problem on the site itself. The fact that you mention that this is an ecommerce site only furthers this opinion and if you are using the default, manufacturers product descriptions for your content then you could have been slightly filtered due to weak or duplicate content.
If you would like to post a URL I would be happy to take a look for you as I have some experience here, alternatively, you can message me the URL if it is sensitive.
I would suggest reading this post from Dr. Pete before you do anything else:
http://www.seomoz.org/blog/fat-pandas-and-thin-content
You can also check the likelihood of content problems with the copyscape plagiarism tool:
http://www.copyscape.com/
Copyscape will show you pages on your site that similar to pages on other sites and it ranks them by likelihood to be causing a problem so again, it can be more evidence that you have been flagged as a weak result and are being buried in the deep, dark result pages.
With anything like this, it's hard to be completely sure and at best you can only be fairly confident about certain things. The job here is to identify any and all problems that MAY be causing the issue and start to work on the problems. From experience, content is often the best place to start so I sincerely hope this helps.
Post a link though, happy to take a look as I am sure many others here are two (with many eyes, you will get much valuable feedback).
Hope this helps!
Marcus
P.S. If you have a content type problem, there is no need to 'ask' for forgiveness, just get rid of the problems and the great and merciful google will cast down a blessing!