Skywest EMB-120 over the busy Bay Area.
Flying a PIC Cross Country flight from Monterey to San Carlos. I was on with Norcal for flight following. However, because of the somewhat low overcast, I decided to take the valley route to my airport (over San Jose, Palo Alto (busy GA airport), Moffet Field (former military base), and within 7 miles of SFO).

Moffet Tower is a federal airfield, and thus there is hardly any traffic, and the controllers rarely get trafffic. All of a sudden I get see this airplane infront of me not moving. Having just flown a full motion airline simulator at the United Training Center, I remembered when the simulator worker put an airliner on a head on collision with my simulated 747, and I remembered how I didn't see any movement. So I dove a couple of hundred feet, when suddenly the Barasilia whizzed over my head going the opposite direction. Right as I started to descend, with the Brasilia maybe 2,000ft from me straight ahead(closing at 300+ kts), the Moffet controller says:
"Cessna 48D, suggest a slight left turn for traffic."
He didn't finish his sentence before the Brasilia screemed over my head.

Look for traffic, even if you are talking to ATC!