Many problems in mechanical engineering, in the linearized case, can be modeled as a second order system of differential equations of type MDGKN, where the matrices correspond to inertia, damping, gyroscopic, stiffness, and circulatory forces. The latter may lead to self-excited vibrations which in general are unwanted and sometimes dangerous. It is well known that circulatory systems are very sensitive to damping and their stability behavior may strongly depend on the structure of the damping matrix. Moreover, it has been known for a long time, that the addition of (even infinitesimally small) damping may also destabilize such systems. The present note studies in more detail some of the effects of velocity proportional terms on the stability of mechanical systems of this type. The aim is to extend the findings recently presented by HAGEDORN et al. Therefore, the analytically derived stability boundary of an MDGKN-system with two degrees of freedom is analyzed with regard to infinitesimally small, incomplete, and indefinite damping matrices as well as the role of gyroscopic terms and the spacing of the eigenfrequencies.