Our X is at Motorwerks right now for the same reason. Right after the superbowl, got a burning smell. Opened the hood to find oil leaking onto the exhaust manifold (left side of the engine). It looked like oil was coming from where the o2 sensor plugs into the manifold, which I know is absurd.

X5 got towed to the dealer yesterday morning. They just got to looking at it this afternoon because of the 20 other BMWs towed in yesterday. I highly suspect the oil seperator and/or breather.