My pld is still pretty low, but from what I've been seeing in my LS, the Plds have gotten bored with the job and are actually leveling blm as a secondary/third job and enjoying it. It really depends on if you personally want a tank or mage job. If you all ready have melee jobs leveled, blm may be a nice change for you.

Don't level blm unless you know you'll want to use it often. If your shell doesn't have many you are going to be asked to go blm more often then other jobs you may have. (out of the handful of jobs I have, blm is requested the most for events so that is what I'm going off of.) If you've all ready sold your quested scrolls, might be good to look the prices up and know what you are getting into. If all that isn't an issue I vote Blm for the fun factor.