You might consider adding some pictures
...eco-hostels are a somewhat new *level... ---level doesn't quite make sense here, I would change with 'type' or 'kind'
...and we have only been able to identify six of them. ---There are many many more in US then six. Simply saying "We have identified six of them" implies you have no done thorough research.
A nice job of linking subjects to other appropedia pages.
I might elaborate on the "for me" part of the benefits of staying at an eco-hostel section. It is briefly touched on and I like it point (it creates a live-in demonstration of low-footprint lifestyle). Are there social benefits of staying at an eco-hostel as opposed to a regular hostel? Cultural? Health?
...What should be considered when planning **to build** an eco-hostel? --- This may reduce confusion between planning to visit or create.
Really like the section of "Why aren't there more eco-hostels in the U.S.? (In our opinion...)" Nice job. Eco-hostels in the US definitely have a reduced market audience. This could be due to the high cost of transportation around the US that I think deters many young foreign backpackers.
Over all nice job, I didn't see any misspellings or grammatical errors