If you are not one of the great Perl Wizards that know the syntax for every commands by heart, you should by this very handy book. This booklet is a reference book. Do not expect to learn Perl from scratch with this booklet (although I learned a lot of details :-). If you do not know Perl I recommend "Learning Perl" first.
The 4th edition of "Perl Pocket Reference" has been enhanced to cover Perl 5.8. It adds some small enhancements for the new IO libraries, regular expressions and Unicode handling. The basics are still as good as in the 3rd edition (although a bit more cleaned up).
I love this book because it is without any useless overhead. The information density is very high so make sure that you read this book slowly.
This book covers "only" the Perl language (which is quite big compared to e.g. "C") It does not cover your favourite Perl module (e.g. DBI, LWP and so on). There are almost no examples in this book. If you look for examples I recommend e.g. "Perl Cookbook" from O'Reilly.
I really like this book. What it tries to do, it does very well (small reference book of the Perl language). I have it always on my desk at work and I already gave away more than 20 copies (German and English versions) to my coworkers.