When we were first getting started, App Engine was just becoming available, and we thought that would be a great platform mainly because of its scalable architecture and Python backend, which both Nick and Scott liked. We incorporated the Spaced Repetition after we read about Supermemo in Wired Magazine shortly after launching.
The idea is to charge users small monthly subscriptions with big discounts for semester-signups. Since a lot of our current users are young and in school it's really important that we keep the price affordable. We've also attended 2 trade conferences in language learning software, and will be going to one more in about a month at which we'll be trying to sell Skritter as a site license to institutions.
If you'd like to check it out in more detail, we've set up a demo account for everyone on HN:
UN: hackernews pass: hackernews
Thanks a lot for your time.