Single walled carbon nanotubes (SWNTs) may be useful in applications ranging from microelectronics to advanced composites. Of fundamental interest in these systems is the manner in which their large length-to-diameter aspect ratio gives rise to anisotropy of other physical properties. Efforts to characterize these anisotropies have focused on creating highly aligned ensembles of nanotubes, but here we describe how weakly aligned samples provide the first determination of bare optical absorbance cross-sections for light polarized parallel and perpendicular to the nanotube axis. These cross-sectional spectra enable accurate and high resolution studies of magnetic orientation in liquid suspensions, which can be used to infer the nanotube magnetic anisotropy. We will discuss how these measurements also reveal ferromagnetic impurities localized to the nanotube, and we will describe our work on comparing the intrinsic magnetic properties of different nanotube chiralities. Finally, single-molecule studies of air-suspended SWNTs demonstrate controlled switching of SWNT optical emission spectra, and underscore the importance of environment in modifying nanotube optical properties.