Not all web sites are created equal...
Anyone can make a webpage. For academic purposes, it is important to always consider the following when using the web as part of your research:
Authority - who made the page? Is he/she an expert in the knowledge that is being presented?
Appropriateness - is the information appropriate for your assignment/research? Consider things like language, age level.
Currency - how old is the page? Is the information itself current? When was the page last updated?
Objectivity - is there a bias to the point of view of the page? Is it hidden or overt?
Purpose - what is the purpose of the site? Does it inform, sell, persuade an opinion?
Dalhousie University has an excellent resource to help you evaluate your web resources.