I bought DOS for Dummies some time ago. It was well presented and covered all the main subjects and suprisingly, the author was really quite funny so it wasn't a chore to read.
I think it boils down to books vs the internet, especially with 'geek' subjects because the '.....for dummies' series is probably covered somewhere out there in google land. Having it all in one place and able to read it in bed is nice, plus you dont have to browse through all the ****.