only thing I did was adding adsense, and added about 100 links in 2 weeks period using ALN.
Before I do these, the site was on page 1 ,around 6-7th, after I do this, it's gone for every keyword.
I googled, and find may people hit by -50 penalty caused by thin content, excessive backlinks.
For me, my site can be considered as think content, as I only have 7 articles ( all unique written by people I outsourced, checked against copyscape).
What bothers me is, before I do much seo, my ranking wasn't that bad, after I did a little seo, it's gone to hell.
So seems to me, if anything triggered a penalty, all the time/money you spent on the site is wasted.