Nothing! Just remember that anyone can post anything for any reason--it's not everyone's goal to share reliable, unbiased, up-to-date information. So, if your professor allows you to use websites for your research paper/project, make sure you critically evaluate them first.
Some of the popular search sites, such as Google or Wikipedia, are fine for exploring a topic you're not familiar with and finding citations to other sources you might be able to use.
Remember: You may be able to find out about an article on the web, but you may not be able to get to the full-text. Often, you'll get to full-text and you're asked to pay for it! If this happens to you, please check the library's databases for the article. If you don't find it there, you can still request it through Interlibrary Loan.