Because everything in it is obsolete as soon as Rails 2.0 ships (very soon).
Will we see the same sort of offers on other Sitepoint books?
Is that true? That everything in the book will be obsolete when Rails 2.0 launches? I sincerely hope not.
If this is true, absolutely hilarious! 
I’m pretty sure that it’s not true that “everything” in the book will be obsolete.
Take a look at the latest (Sitepoint) Debug Ruby Article which explains a bit more. http://www.sitepoint.com/article/debug-rails-app-ruby-debug
Interested in others thoughts . . .
Yes, this book will be perfect for you.
How could Ruby 2 make all previous Ruby books obsolete???
Yes, it should have improvements and additions, but the basics should stay the same. The older books will simply not sell very well. And being cynical, I’ll bet the new book concentrates on new features and so if you wish to learn them because you got hooked via the first (free) book, guess what, you’ll buy the second book.
Which is still better than buying the first book and then having the more advanced new one appear a few days later.
^ Dr.John is right of course, it’s very clever, but not necessary by any means to offer free books. Still, from what I’ve read so far, it was a very good idea. I really hadn’t heard much hype about this framework, and i’ve done some research on a few, but the book will no doubt prove very useful forgetting any proposed new version of rails.
90% will probably download it and never try to read it…
But… Thanks a lot… 
For some reason I’m not receiving the download link at all. I’ve tried two different addresses and the emails are not in the Junk either.
I received the download link but it doesn’t load. Firefox just sits there for ages trying to load the page before giving up.
We’re seeing a couple hundred concurrent requests for the PDF right now, so you might have to try again in a little bit…
Update: We’ve experienced massive demand for the PDF with up to 200 simultaneous downloads! As a result we’ve moved the file to our Amazon Elastic Compute Cloud (EC2) to help deal with the demand. This is in effect now so those who’ve had trouble downloading should give it another go.
My download worked. Thank you for this
That really stinks for the folks who bought it yesterday - but for those of us who bought it months ago who cares?
Things change - marketing methods change, etc…
It’s a great book for beginners and a smart marketing move on sitepoints part. I know I’d rather have a paper bound book any day.
Bummer… that kinda bites cause I just paid full price for it… wish a different book was free. Oh well… good book by all means.
Well thanks for the book!
I’m curious as to how much it will affect book sales as people wait in hopes that it’ll become free.
This is excellent! Thank you so much! 
Awesome! Thanks Sitepoint! I’ll show this to our development team.
Haha, well now I get it.
There is 5 pages of advertising scattered throughout the book.
I wonder how much the advertisers are paying/download.