The Los Angeles Times is reporting that the "top kill" effort appears to have successfully stopped the flow of oil and gas from the well.
According to U.S. Coast Guard Admiral Thad Allen, engineers were able to inject heavy drilling mud into the well head and stop the flow of oil for the first time since the incident began 36 days ago. If the mud holds, engineers will then inject concrete into the well to seal it.
-- UPDATE 3:48 pm PST --
According to various news sources, BP's top kill effort was suspended at midnight last night. There's no word yet on why BP suspended the effort, only that efforts to plug the well have just begun within the past hour.
-- UPDATE 4:08 PST --
In viewing the live cam it appears that the oil is continuing to spew forth unabated.