This is one of the issues that I would like to address and it is very common these days.So what is this +30 Penalty and +50 Penalty by Google? It is basically Google trying to remove spams and bad contents using this penalty but at some cases these penalty might go wrong if you are unlucky.This penalty is awarded by Google if you build sites exclusively for search engines and not for readers.For eg. if your keyword density is very high and you are consciously putting in effort to get ranking for the keyword by adding it in your site content it might well trigger the penalty.I have myself experienced it and I recommend people to avoid it.Also don't build links quickly and aggressively for new and not well established sites.Google does use something called trust factor to rank sites.So make sure to gain the trust first by getting links from good sites and linking back to good ones.Then link building process should start.Avoid adding a lot of duplicate contents.Though this is not proven to be the cause of penalty but avoid it at any point as this against human TOS.Make sure to follow the Google webmaster guidelines before doing or building any website.Avoid site wide links as in some cases this had triggered the penalty.Please post your comments regarding this below.