Ming reportedly informed the league office of his decision sometime within the last 48 hours.
Yao Ming has been constantly injured over the past few seasons. It appears as if the lingering wear-and-tear of the NBA has finally caught up to the 7'5" big man from China.
My speculation is that Yao will continue to rehab, with the possibility of a comeback. Any comeback would most likely start with a re-entry through the Chinese Basketball League first.