I'm going to go out on a limb and assume that looking for someone who you consider to be 100% compatible (and by compatibility i mean like in areas of attraction, intellect, values, goals, humor, world-view, etc - the important things) is un-realisitc.

Where would you draw the line? 90%? 80%? 75%?

How "compatible" do you consider yourself and your SO together? How do the two of you deal with the areas where you are "less compatible"?