Hi,
The last six months, I've been busy writing "Linux aux petits oignons", a general introduction to GNU/Linux. The book is aimed at the beginner (or intermediate) reader, though :
1) it's *not* based on Ubuntu, but on CentOS 5.3 2) it doesn't shy away from explaining basic UNIX concepts 3) it favours the use of simple command-line tools
Here's the editor's page :
http://www.editions-eyrolles.com/Livre/9782212124248/linux-aux-petits-oignon...
And here's the book on Amazon :
http://www.amazon.fr/Linux-Petits-Oignons-Apr%C3%A8s-Windows/dp/2212124244
It's 550 pages thick, but you can (almost) read it like a novel.
Enjoy !
Niki
PS : for those who wonder, "Kiki Novak" is my pen name.