I use a thin knife blade to pry the limpets off the rocks; it's easier if you catch them unaware, since they cling even harder to the rock once disturbed. The one time that I tried boiling any quantity of limpets they turned the water and the sides of my pot a light green color, and gave the water a faintly unpleasant smell. Although they tasted fine when cooked, I wouldn't add them raw to my soup pot, for fear of tainting my soup with a green scum. Cooking them seperately would avoid that problem. Boil them for 3-5 minutes.

Next time, rather than boiling them I'll try cooking them in their own juices in the shells. The challenge will be to arrange an sufficiently large cooking surface in the wild. There's not much meat in a single limpet, but they're pretty easy to gather in quantity!