If you hit a penalty your site drops by 50 positions. got popular as the minus 50 penalty. This means a particular page(s) dropped by 50 positions because of over-optimization for the keywords that the page has been linked to, be it externally or internally.
i never heard about this penalty..domain penalty and sendbox...i think excessive link building i the main reason penalty
This is the first time I have heard about this kind of penalty. Over optimization?? Do u mean to say i have to limit my SEO work process to avoid this kind of penalty? No way! This penalty will be arised when you do wrong way to optimize your keyword like black hat, cloaking etc.
even I have never heard of 50 penalty.. I follow one simple thing and that is white hat... though it take times..
Google - 50 penalty means your search visibility will be drops from position 1 - 50 positions. There were many factors for Google penalizing. There may be you trying keyword stuffing, may be you some pages not found, broken links, bound rate high, unorganic techniques or some other factor.