Wikipedia is a highly successful example of what mass collaboration in an informal peer review system can accomplish. In this paper, we examine the role that the quality of the contributions, the experience of the contributors and the ownership of the content play in the decisions over which contributions become part of Wikipedia and which ones are rejected by the community. We introduce and justify a versatile metric for automatically measuring the quality of a contribution. We find little evidence that experience helps contributors avoid rejection. In fact, as they gain experience, contributors are even more likely to have their work rejected. We also find strong evidence of ownership behaviors in  practice despite the fact that ownership of content is discouraged within Wikipedia.