Sony Ericsson released new feature for Cyber-shot devices: Smile Shutter™. I think this feature is imported from the famous Sony Cyber-shot camera, which have been implemented in many T-Series camera. Smile Shutter™ will help you to capture a smiling face. When the person in focus smiles, the camera automatically takes a picture. You can override this function by pressing the camera key a second time.
Smile Shutter™ will be available on latest Sony Ericsson Cyber-shot phones: Kate (C510), Filippa and Frances.