Looks like a good resource for teachers, but may be difficult for younger students to navigate.
I have not used this website in my classroom, however I can invision how HippoCampus could be useful in my instruction. It appears that you can easily create an account with HippoCampus to help organize your videos into a playlist. Then, you can share your lists with other users. This is a great way to organize helpful videos. However, to simply watch videos, it does not appear that you need to sign up for an account.
After exploring the site, I would imagine that this website was designed for older students rather than younger ones. Perhaps middle school or high school students would find the most this website most helpful. My elementary students would likely have some difficulty navigating the site.
When I most recently explored this site, I found video content to be organized into four categories: Math, Natural Science, Social Science, and Humanities. The majority of videos that I watched provided solid explanation, but little if any actual practice for students. Also, some videos required users to download them. This extra step could be less inviting for some students. Finally, I found some of the videos to be outdated and dry. These videos quickly lost my interest, as they would students' interests.
How I Use It
If I were to HippoCampus with my students, I would use this website as a tool for students that are in need of a different approach to learning a concept. HippoCampus offers tutorials and videos from multiple sources such as Khan Academy and PhEt. If a student is struggling with a concept that has been taught in class, perhaps he could use HippoCampus to search for various videos or tutorials to help him better understand a subject matter. HippoCampus could also be for whole-group instruction. Find a video or tutorial on HippoCampus and then show it to the class as a way to preview the content that students will learn.