I own and use about a dozen 21 days/ 24 hours books and love them!
When I am learning a new language I find they are a great place to
start. Sure I know you can't LEARN a language in 21 days but you can
get a reasonably good grounding. And as far as the problems (real
world versus text book stuff) anyone who thinks that an example out of
a book is going to hold up in the "real" world, well, they should be
reading the "For Dummies" books. Many of the examples are just that:
silly examples that are supposed to illustrate a technique or a
construct NOT teach you how to build a shopping cart app or a
bio-sensor or anything.
 Anyways, I like them, just realize their limitations.
PS: If I want an in depth book with more "real world" examples I go
for O'Rileys or even some of the "...Bible" series or even (though
carefully) Sam's "Unleashed" series.
George K