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? 
Al dente cooking is a transitional state that lasts for a very short amount of time (one minute longer in boiling water makes pasta too soft, one minute shorter and it's still crunchy). For this reason, authentic Italian pasta packages state a precise cooking time, which is very reliable to make a good al dente pasta. A cooking time interval (e.g. "7 to 10 minutes") is usually given to accommodate to other countries taste, who may prefer a softer pasta, and therefore its presence could be a good indicator of an Italian look-alike pasta brand. In this case the lower figure indicates the al dente cooking.  Lacking this information, a good cooking time can be figured by cross section size, length and shape of pasta: obviously, thicker and squat formats require more time. Complex shapes, such as farfalle, can be trickier because a thick core could reach the al dente cooking while the thinner edges are already too soft.  As a rule of thumb, cooking times for common pasta formats are:   Long and very thin (spaghettini, bavette): 6 min Long and thin (spaghetti, linguine, bucatini): 8 min Short and thick (maccheroni, rigatoni, fusilli): 12 min Small and thick (farfalle) : 8 min Small and thin (pasta usually boiled straight into broth): 6 min   These cooking times apply only for dry durum-wheat pasta; other types (such as fresh egg pasta) usually have a shorter cooking time.  After straining the boiling water, pasta continues to cook by its own heat; for this reason it has to be eaten as soon as possible. Only for some Italian regional recipes (typically pasta boiled straight into a thick vegetable juice, e.g. pasta with beans, pasta with potatoes) you may want to let it rest for up to 5 minutes after straining to let the juices coagulate.  Also, for recipes where pasta has to undergo a second cooking after boiling (e.g. stir frying in a pan with vegetables, shrimps, mushrooms, etc.) a better result is obtained by boiling pasta just one minute less than the cooking time given on the package. 