I like the concept overall. The animations you get when you misspell a word are pleasant and informative. I didn't register, so this feature might be there, but it would be nice to always be able to see "percentage right" after completing a set of words, or some hard numbers you can compare over time. Also, is there any evidence that this will make you a better speller overall? Or will this simply help you spell words that you have spelled incorrectly on this site previously?