I presume you have to be a member of their Prime service to get these as they all show as costing rather than free [just assuming I've missed the bleeding obvious!]
Its not on Amazon - I got the link form a photography blog email.
EDIT - Just realised perhaps I shouldn't have posted it here as its not a Kindle book..
I was working earlier when I grabbed v2, so I imagine it will be back after the maintenance.
Many thanks for posting those.
I went to search for free books and found this article:
http://www.wired.co.uk/news/archive/2013-01/10/freebook-sifter
which came to this website:
http://www.freebooksifter.com/?c=43
looks useful and a sustainable updated list for such deals.