Free is good.
Free, plus is better.
No, this is not some off hour slicer/dicer/come on, although the effect is about the same.
They get permission to market to you in this case for free.
(The slicer/dicer costs real money.)
Tom Friedman, NY Times author, has a new book coming out. How do you catch attention of potential readers?
Provide free downloads of the audio version of his most recent book "The World is Flat". This also entitles you to a teaser audio sample of the new work: "Hot, Flat and Crowded"
You can sign up for this here. The offer has a limited time period; the free downloads begin 7/25 and expire 8/4/08.