The first thing you show is a signup page. Why would I sign up if I find no value in the site?
"Where the world comes to learn"
If it's a forum, learn from stackoverflow, reddit, 4chan, etc: give everyone your content, and if people find value and want to contribute, they'll sign up.
Good point, actively contributing answers certainly helps practice a skill area. But I can't imagine thinking, "I need to practice tree traversal algorithms: to Stack Overflow!"
A site with free, open, community driven practice problems and solutions. Sort of like a wikipedia for questions. I could imagine this being a key ingredient in the future of OER. Would be cool to see something like this integrated with http://metacademy.org
"Where the world comes to learn"
If it's a forum, learn from stackoverflow, reddit, 4chan, etc: give everyone your content, and if people find value and want to contribute, they'll sign up.