People who knew me as a full-on vegetarian in the past might be surprised that I now cook live crab and lobster. But they are so delicious when freshly cooked! And although I am still completely against factory farming, I can still enjoy meat now and then without feeling too guilty: buy local, buy organic, and where possible, buy from people you know and make sure they are treating the animals well.
As for this crab ... I actually have no idea where it came from. But it goes on sale very few times during the year and so I had to take advantage of the low price.
Putting them in the freezer for 20 minutes or so before cooking will numb them a bit and they won't move much which makes them easier to handle. If you want to believe it is more humane, well, think whatever you want. But if you are worried about that, you probably shouldn't be doing this in the first place.
When serving, assume one crab per person. The dungeness crab found in stores tend to be about 2 lbs apiece which yields about 8 oz of crab meat (so 25% of the total weight). And always consider cooking an extra one or two for leftovers.
I don't cook crab often so don't feel I can offer advice on how to clean them for guests. The few times I've done it are with good enough friends that you just plop the crab on the table (after spreading newspaper down) and let everyone work it out for themselves.
You need a very large pot - a 12-litre stock pot should be good for 3 crabs. I have to admit mine was a bit short on size so they were kind of crammed in but I made it work. Make sure you bring the well-salted water to a hard boil.
Cook about 15-18 minutes. Remove from boiling water and plunge into a bowl of ice-water so the meat stops cooking or it might get rubbery. It doesn't need to sit in the cold water long, just enough to cool it down.
Then serve immediately. Crab always goes well with potatoes and corn (add sausage and you've got yourself a Southern crab boil). Serve with lemon slices, garlic butter or this Harissa-Lemon Butter (I saw something similar used as a steak sauce and knew it would be delicious with seafood):
5 Tbsp butter
1 Tbsp chopped flat-leaf parsley
1 clove garlic
3 tsp harissa