My Take
Overall I love this site. It offers a wide variety of ideas, support and knowledge for students and teachers. It is a great support for science fair projects as if offers well over a hundred different ideas with a step-by-step guide. It's also free and available to anyone out there. It offers a section to ask for support from experts and allows students the chance to explore science careers as well. One negative would be that there is a lot of knowledge there and you need to take the time to explore and not expect to jump in and out quickly.
How I Use It
I could see using this site in an upper elementary, middle and high school classroom. If I worked in those grades, taught science and/or had a science fair this site would be a great resource. It has a large number of project ideas so students won't overlap with their project concepts. It offers a place to ask for support from an expert. I could also see using this if you were focusing on various science careers as they have an entire section on various careers associated with science.