Looks pretty good so far, although I have a couple of suggestions:
1. The kana pictures on the learning mode should probably be bigger - there's quite a bit of wasted space there. It would also be cool if the learning screen had an option to move through the kana automatically.
2. The test mode is a little slow - it would be better if it went to the next kana immediately after ejecting the previous one, to keep the pace up. In addition, it would be more convenient if you could enter the transliteration of the kana by pressing the enter key from the text box instead of clicking the button.
Anything that helps people learn Japanese is great in my opinion, so keep it up!