I've been using the grading buttons for writing characters/words for about 5/6 weeks and I like it a lot. I wish I could do it for tones as well, because sometimes I'll come across easy characters like 火 and I wish I could mark it as "easy" so that it comes up a lot less.

Here's a related question: Suppose I come across a character like 国 and draw it out and then mark it as "easy". This will result in the character coming up again at a later date than it would have if I hadn't marked it "easy" ．If the next time it comes up, I mark it "easy" again, will I have to wait an even longer amount of time before it comes up again?
Example:
1.国 comes up on 10-31-10 and it's marked "easy"
2.国 comes up on 11-31-10 and it's marked "easy" again
3.When can we expect for 国 to come up next, based on this example? (ballpark estimate)

Because it takes so little time to do tone prompts, and because the grading numbers/buttons conflict with the tone numbers/buttons, we decided it was counterproductive to allow finer grading on the tones. It would take longer to think about it and grade them as "too easy" than to just do them a little more often.

In that example, it varies depending on a lot of factors, but maybe about six months.