How to determine what's turning people off about your service?
patio11: Are you collecting email addresses?  You can presumably figure out which users have not logged in in a week.  Send them an email saying "Hey, this is George from Skritter.  My friends and I are trying to make the best thing ever for Chinese language learners.  We'd really appreciate if you could give us two minutes and tell us what you think, so that we can fix the problems students learning Chinese are really having.Regards,George"P.S. A/B test response rates with inclusion of a picture.  I'm guessing they're off-the-charts better with one, but you know what they say about guessing.