One criticism of the levels; there should be automatic browser resizing. I have a small screen, so I had to scroll down to see all the possible answers, and then I couldn't look at the word and what the character looked like at the same time I was searching for the definition.
Also, for the part of the learning where you type in the pingin, it doesn't read English language characters as correct unless they have the little symbols on top of them. I can't find those characters fast enough to type them in!
Sorry for the sizing trouble, we'll definitely have to get better with it.
For pinyin input, there's a page that explains the input system linked to at the bottom, though we need to make it a bit more prominent. Basically you type a number 1-5 after each syllable to apply an accent to it.
Also, for the part of the learning where you type in the pingin, it doesn't read English language characters as correct unless they have the little symbols on top of them. I can't find those characters fast enough to type them in!