One thing I'd like to see is clear, unambiguous examples. Time and again I encounter examples of some concept, done in a Perlish way that wholly obscures the intended point by including features besides the one being shown. As a brand new Perler (but a long-time programmer), I find this quite frustrating. I bought just about every O'Reilly book on Perl I could get my hands on, and they all seemed to have this problem to some degree.
I think part of the problem is Perl's unique ability to do so much with so little. It's tempting to write multi-faceted examples - in fact, it's hard not to do otherwise. This is great when you're writing a program. It's not good when you're illustrating a point.
So, what I missed were simple examples that displayed one single aspect, and didn't combine several tricks into one short expression. The various tricks are important to know, and often will save time once you know how things work. But from the standpoint of a newbie, they simply confuse, making it that more difficult to grasp the one concept under discussion.
One other feature I missed in books was a simple listing of the various functions, operators, etc. in Perl with a short summary of how they work. This is easily taken care of in perldocs, but it would be nice to have it in book form. I like to read this stuff, and sometimes I don't have a computer handy.