Did you know that IF is in the middle of the word LIFE

About "symmetry";

When making, say a nurbs-circle-curves, for making the fuselage of an airplane... I usually tweak the vertices in pairs to keep the symmetry... This is done with the move and scale tool... And afterward, when I am making parts to fit to the fuselage, I usually only model one of the sides and then duplicate the parts around an axis, by typing -1 in the appropriate place in the duplicate options menu. Then the parts will fit exactly on the other side of the model.