Are disulfide bonds a major force in determining the tertiary and quaternary conformation?  For this class, No!  However, the matter is highly debatable.

Under Chapter 7, V, Quaternary Structure, the text tells you that the subunits of quaternary proteins are held together by the same types of forces that hold a monomeric protein together in their native conformation.  The contact regions between the subunits of globular proteins are closely packed and made up mostly of hydrophobic residues [Hydrophobic Interaction].  Hydrogen bonds are formed between the backbone and R-groups of different regions of the polypeptide chains.  Occasionally a salt bridges or salt bonds are formed.  The subunits [of globular proteins] are very rarely held together by disulfide bridges and never by other types of covalent bonds. (p101, 3rd edition).  The disulfide bonds may stabilize the tertiary and quaternary conformations of proteins but they do not cause the structure to develop.  That is, the structures are usually fairly stable without the disulfide bonds.

Earlier in Chapter 7, IV, Tertiary Structure it states that the forces that maintain the tertiary structure are H-bonds, ionic bonds, van der Waals interactions, hydrophobic effects and disulfide bonds formation.(p 98, 3rd edition).  This would indicate that disulfide bonds are important

Figure 6.12 notes that insulin is held together by disulfide bonds and may appear to be an exception but not if you realize that the subunits were formed in a single protein and the conformation of that protein was not determined by disulfide bonds.  Figure 7.15 shows the structure of immunoglobulin held together by disulfide bonds. Again, the conformation of the subunits were not determined by disulfide bonds. Collagen and other fibrous proteins are often held together by covalent crosslinks. None of these proteins could function without disulfide bonds.