Netflix has announced that those who requested the free discs needed to launch the Instant Stream service on PS3 will receive those discs starting tomorrow. Additionally, Netflix announced the service will start as soon as the discs are received.
Whether a PS3 update is required hasn't been announced. The service is using a disc to stream the content due to exclusivity contract with Microsoft for the Instant Stream service to stay on Xbox 360. Likely, the disc will be ditched once that contract expires next year.