I've just used Learning Perl as a text for a course on bioinformatics for biologists, none of whom had programmed before. They found the book very difficult to read for beginners, as it DOES presume some knowledge of programming, preferably in C (not as bad as the Camel book, however!). I kept wishing for more and better introductory examples in the text, and some of the Exercises at the end of the chapters were a little obscure. Simpler exercises might be better.
I love O'Reilly books and recommend them to my students - but next semester I will be switching to a newly published book on Perl aimed at true programming newbies.