I find perldoc to be a valuable asset in my class. I personally don't find it as easy for people to read as Learning Perl, but I always make sure to supplement my lectures and discussion with perldoc references. I feel I'd be cheating students out of a large part of their education otherwise :)
I'm really glad you use perldoc in your classes. Probably the most overlooked *gem* in Perl is the perldocs, IMHO. Probably like most people, I used perl for a few years before someone clued me in to the perldocs. Since then, it's usually the 1st place I look for an answer to any perl question. I'm sure a lot of time and energy went in to writing the perldocs - they are a very usable resource, even for newbies.
Like the saying goes, "Give a person a fish, and feed him for a day. Teach a person to fish, and feed him for a lifetime." Perldocs rule!