We investigate the significance of secondary effects caused by free carrier accumulation and subsequent heating on the nonlinear behaviour of ultrasmall Silicon-On-Insulator ring resonators. All-optical bistability based on thermal dispersion was experimentally obtained for an input power of only 0.28mW. At higher powers, pulsating behaviour was observed which is problematic for the stability of thermal memory and switching operations. Using free carrier dispersion, we also demonstrate all-optical wavelength conversion with a pulse length of 10 ns, indicating that bitrates of 0.1 Gb/s are feasible. Also here, the presence of unstable pulsations was observed, leading to significant errors in the converted data pattern.