In my first few months of using Perl (back in 1995), I cannot tell you how much time I would have saved if I had known about this option on perldoc. Initially, I was learning by adapting code that someone else had written, so in the course of a day, I ran "perldoc perlfunc" repeatedly to look up the details on function calls, and I was constantly paging down to the function of interest...
UPDATE: On second thought, I have to admit that I learned a lot more about perl (and grew to appreciate it more quickly) by virtue of spending so much time with the "perlfunc" man page.
If you define PERLDOC_PAGER=less or PAGER=less in your environment, say in .bashrc or the equivalent, it works fine. Otherwise perldoc will use more as a pager, which works, but doesn't know how to scroll backwards. That's sad.
It all depends on your unix environment / version of more. HP-UX more handles paging backwards just fine, for example. I would agree that not being able to page backwards is a pain, but it is not a generic more problem, but rather a problem with the more program on specific distributions.