but the "in 21 days" part makes me suspicious whether it's any good

As a book to get an overview of the language as such it is maybe ok, as it covers most of the basics, but as I feel, in a semi-random order and skipping lots of important parts. The really bad part is however, that once you've finished with it, it is of no use any more, as it virtually impossible to use it as a reference - because it lacks an understandable structure and has no good index.

This is pretty harsh claims, so I wish I could back it up with examples, but I gave that book away to someone at work.

I bought it as my first perl book, and in all honesty, I learnt more from Perl 5 pocket reference. Then I bought the Camel and all was sunshine again.

I don't know if this should be a disclaimer or another argument against the book, but before Perl I had been programming other languages and worked as a developer for some time. That may affect what works or not I guess.

This is only how I experienced it, I am sure the book has been very succesful in helping others. For me, I'll never buy one of those "Teach yourself in X Something" again, and never anything from SAMS.