We demonstrate a high-speed multi-functional spectral-domain optical coherence tomography system, using a broadband light source centered at 1.3 microm and two InGaAs line scan cameras capable of acquiring individual axial scans in 24.4 micros, at a rate of 18,500 axial scans per second. Fundamental limitations on the accuracy of phase determination as functions of signal-to-noise ratio and lateral scan speed are presented and their relative contributions are compared. The consequences of phase accuracy are discussed for both Doppler and polarization-sensitive OCT measurements. A birefringence artifact and a calibration procedure to remove this artifact are explained. Images of a chicken breast tissue sample acquired with the system were compared to those taken with a time-domain OCT system for birefringence measurement verification. The ability of the system to image pulsatile flow in the dermis and to perform functional imaging of large volumes demonstrates the clinical potential of multifunctional spectral-domain OCT.