Asphaltenes are molecules which can undergo a thermodynamic liquid-liquid phase separation from sufficiently paraffinic solutions. The asphaltene-rich phase thus formed often has a high glass-transition temperature, and thus a fractal morphology results. Here, we report temperature and time-dependent neutron scattering studies which elucidate the solution behavior of asphaltenes. The temperature-composition dependence of the asphaltene precipitation phase boundary is shown to be consistent with that expected due to solution theory. We report temperature- and concentration-dependent viscosity data which demonstrate that the high viscosity of asphaltene-containing systems is due to their proximity to the glass transition and the reduction of viscosity with dilution is no more than a plasticization effect, or a reduction of the glass transition with dilution.