If you're a Netflix subscriber and asked for a disc, Netflix has already mailed them out, and will get into most people's hands by tomorrow. The PS3 will then join the Xbox 360, the Roku, TiVo DVRs, some standalone Blu-ray players and of course the PC as devices which can access streaming video through Netflix.
Netflix claimed recently that nearly half of their subscribers have used the streaming service within the past three months. That's a substantial amount, which is good news for those that pay for the service -- it means that Netflix will no doubt have a keen interest in expanding it.
Though the online movie market is still arguably in its infancy, Netflix clearly has a huge advantage over existing and potential competitors, such as Amazon and Hulu.