I can recall at least 3 startups (non-YC funded) which announced their launch here and went on to gain traction and good blog coverage. The quality of the product speaks for it self really. Some have been good, others weak. Regardless I dont think it has any affect on credibility of others announcing their launch here. The goal is just to show people what you've built and get feedback, right? If a product is truly good, it will gain dedicated users and begin its viral spread.