I've tried a number of different ways to tell when spaghetti, capellini and other pasta types are done, but I'm curious if there are more specific rules of thumb. With regular spaghetti, I've tried biting-in-half to see if it's still white in the middle, throwing it against the fridge (which seems more amusing than useful), etc., but are there better and more reliable ways?

Also, how much does pasta 'cook' once you take it out of the water? So if you want an al dente pasta, do you take it off slightly before done? If so, how much?