As I only had some passing familiarity with a unix environment when I started learning Perl, I can attest to the veracity of your first point. On the other hand, when I needed to gain more unix chops, I found my Perl experience very useful.

On the second point, PBP is a good starting place for standards that a noob could refer to. I wish it had been out when I started. I wouldn't have had so much to unlearn.