Harpoons figured prominently in a recent effort to kill an uber-twinked evil boss in our campaign. He was a Bone Knight (lots of immunities) with enormous AC, very high saves, evasion, mettle, wielding Souldrinker (!), with a group of helper casters. Also, and here's the stickler, he used the feats Karmic Strike, Sidestep, and related effects to make him basically unhittable in melee combat.

Solution : Surround him with very strong Earth Elementals, each having drunk a Heroism potion (granting the feat Brutal Throw). Each of these tosses a harpoon into him which has been enspelled with Brilliant Enery. Each elemental pulls straight out, so that he can't move without spending at least two full rounds pulling out harpoons. Our party beefcake tosses a barbed net, also Brilliant Energy, onto him from a distance of ten feet. One of our casters dispels the net, causing it to become an ordinary barbed net, enmeshed with all of his gear and armor. Beefcake pulls with all his might, pulling all the boss' gear right off.
When a Bone Knight's armor is removed, he dies.
Such a pity, then, that when we actually managed to get all of this together, we were facing a polymorphed mook.