If you click on the link Submit Screenshot, the URL is not found because it starts ".jmonkeyengine…" (with the www). If you manualy enter the URL correct to be "www.jmonkeyengine…" it takes you to a random blog post.
Yes, the screenshot submission is currently broken… That link used to point to a blog page where you could 'upload your screenshots', though it was unworking when we switched to Wordpress-MU, so it was not carried over. We've been toying with implementing a new gallery system that would re-include this functionality as well as some other features, but more effort has been going to improving the wiki and forums as those are the main sources of information.
That said, this doesn't fall on deaf ears :) Thank You.