What a cool application. I would love to be able to use it without paying when you do launch. I find that learning Chinese on there becomes enticing, and there is a certain feeling that I am playing a game. I don't think it would hurt to have a ten character demo on the front page with a full tutorial for the Chinese and computer illiterate. That may hook inidividual users, especially if you can buy in at a good rate for starter packages. It seems like you guys are trying to exclusively appeal to the very intent on learning Chinese people, but even from your testimonials it seems that Skritter is a good pass time, even for those not studying Chinese and just want an easy, fun way of drawing chinese letters. I think offering a startup package for cheap will draw a lot of people, and as I have found out, you will soon get hooked.
Also, it may be sweet to add little quiz games to Skritter. Like timed strokes, or something fun (you appear to be creative) to really entice people and motivate them to move on to the next lesson. It always feels better to conquer something like that in an online learning app... And finally, please tell you guys are planning an iPhone app?