You should try http://lrnj.com . It automatically guages how you're doing with the kanji you've already covered and presses forward or reviews depending. It's done up as an RPG and the enemies are constantly hitting you while waiting for your answer (instead of using a fixed time limit). Overall, I find the learning system to be very refined and the program to be quite effective. At one point, I was up to 800 Kanji, but Having not used any of them in over a year, I've since forgotten most of them