Yea, I think there's definitely some high-quality lessons on
lojban.org already, and more good ones being produced on google wave as well. I see the two approaches (lessons and submitted sentences) as being a pretty solid model; there's two more things I think might complete the system:
Rich dictionary entries
I think that the idea to show rafsi in practical use is great; and I think the best way to flesh out gismu entries (and cmavo, eventually lujvo too) is to have dictionary entries that can have example sentences and comments/questions, a record for common questions that people have about usage etc. The entry for each word could (should) have rafsi examples if applicable, natural language origins if applicable, and example usage (possibly more).
Flash Cards
If people get the initiative to make flashcard groups for lessons, just make them and link to them on
smart.fm, which seems to be the best free platform-independent flashcard solution I can find. The only things that come close are jar files (like jMemorize) or not as flexible or intuitive as
smart.fm.
I like Quizlet and use it a lot. Why do you think it's not that good?