Lessons in each Skill
I think it would be great to see a well-written introduction to each Skill. Users could write introductions themselves, and other users could vote, so the best introductions would be displayed at the top of the page. This would massively help me to understand grammatical issues and get a general feel for topics; this is hard to achieve through just seeing and writing sentences.
For example, it's impossible to learn about the difference between formal and informal verbs without someone actually telling you. An introduction could identify some of the words you'd learn as well as explaining why certain phrases exist and in what situations you'd use them.
I agree. I find it odd that DL has apparently not taken notice of all the people thanking others for referring them to sites like www.studyspanish.com. There are some that think that a purely inductive approach is best, but I disagree. Nothing wrong with at least offering information/explanation of basic grammar and syntax, IMO.