Today we (my husband and two children) had a trip to the London Aquarium, my daughter just wanted to find Nemo and Dory, but my son was fascinated by the jellyfish, including whether they really do sting. Having been stung by a jellyfish previously I could very much confirm they do sting and it is painful, however nice they may look floating around their tanks!
My brother got stung by a jellyfish once too, he had the tentacle of a jelly fish twisted round his arm... he was pretty sick!