The Solar Mass Ejection Imager (SMEI) was launched into a Sun-synchronous orbit in January 2003. Its mission objective is to detect and track coronal mass ejections (CMEs) from the Sun in order to improve space weather forecasts. In the three years since launch, over 200 CMEs, about 30 of which were Earth-directed, have been observed by SMEI. We have been able to track several of these CMEs from the SOHO LASCO coronagraphs ($<$8$^\circ$ from the Sun) through the SMEI field of view ($>$20$^\circ$) out to 0.5 AU and beyond, and to observe the morphology and evolution of distinctive features over this wide distance range. We report on comparisons of measurements of CME parameters made in the inner heliosphere with the more typical measurements made nearer the Sun with coronagraphs. We illustrate SMEI's capabilities and present key statistical results on basic CME parameters and the use of SMEI-type data in space weather forecasting models. For example, timely observations by SMEI of CMEs en route to Earth could be input to DoD's operational Hakamada-Akasofu-Fry solar wind model to correct or refine its real-time forecasts of approaching disturbances.