If they could add some Asian languages, at least Korean which uses an alphabet and would probably not require as much special dev as something like Chinese (mandarin) would, that would be super sweet!
Prior to having seen Duolingo, I started a service that is similar to Duolingo, but only for Mandarin Chinese. It's only free for the first 60 words (then $5.99/mo), and I don't think the proposition is quite right yet. It's at http://fastchinese.com if you'd like to check it out.
