I can only tell you what I know. I know that I was selling between 450 and 550 ebooks a day on Amazon when I got as low as #65 on the top 100 bestsellers on Amazon.com. I was hovering around #130 when selling 250 books a day.
A Knight in Central Park was released on Amazon on 3/18/11 and is ranked 172 as of today (4/21) and I sold 250 books yesterday (4/20).
Return of the Rose was released on 3/2/11 and is ranked at #1,667 as of today (4/21) and sold over 50 yesterday (4/20).
I tend to make the majority of my sales after 5 PM each day and on the weekends.
Let me know if you have any questions! I have to go get my hair cut, but later on today I plan to talk about how many books I've sold at B&N. :)