As a counter-point to the grandparent, this discount convinced me to purchase. I hadn't heard about the previous discounts.
I bought the bundle. I didn't buy it before because I'm not yet certain when/if I'm going to learn Ruby on Rails. Currently learning Python and web programming with Udacity, and finishing up some other projects.
But I'd heard such good things about your book that I had already planned to buy if I ever committed to learning Rails.
This discount tipped me over the edge. Having the book + screencasts on hand is a strong inducement to work through them, and 40% is too good an offer to pass up.
In my mind it hasn't reduced the value of the book at all. A discount for a special occasion seems distinct from a discount for other reasons. I saw all the other discounts on the HN front page and mentally lumped them together with yours.