I have to say depends on the book, if it is something I am desperate to read, then I would pay anything. Say a new Game of Thrones book. But for a book that was going into my HUGE slush pile of waiting to read, then I would wait for the price to drop. I can only read with an ereader, paper is no good with my vision. I have brought more than 300 books that I still have not read, and have about 50 in my wish list that I am willing to wait on a price drop to purchase. Off the top of my head there would be less than 10 books I am waiting on to be published that are in the now now and right now at any price list.
But the reality is it is no different than if it was paper, those must have now books are the ones I would snap up day of release as a hard cover.
As I see it I am just paying day of release price in a formate that works for me.