I wanted to just download it too and had the same feeling when confronted with the slider, but I don't want to pay for it as I don't know if I'd actually get around to reading it. My choice was just not to consume it at all rather than offend the author and out myself as a cheapskate by taking it for free.

Not sure if this is rational, but it's an interesting reaction.

I'd be interested to see stats comparing the bounce rate and revenues from this experiment to a) regular paid downloads, b) direct free download link with no slider.