CAPT OF A DC10 OBSERVED A SEL ACFT NEAR SAME ALT JUST OFF THE ACFT NOSE DURING INITIAL CLBOUT AFTER TKOF FROM A CLASS B ARPT. NO EVASIVE ACTION WAS TAKEN; BUT WHEN THE CAPT QUERIED APCH CTLR REGARDING THE LIGHT ACFT; HE WAS ADVISED THAT ATC HAD BEEN TRYING TO CONTACT HIM FOR A TA. CAPT REALIZED HE HAD BEEN ON TWR FREQ AND NOT SWITCHED TO DEP CTL.

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SHORTLY AFTER TKOF; SFO RWY 28R; WERE LEVELING AT 3000 FT TO RAISE THE FLAPS WHEN I SPOTTED A LIGHT PLANE (SEL) ABOUT 11 O'CLOCK. SIMULTANEOUSLY I SPOTTED A BLIP ON THE TCASII AT -400 FT. I STARTED TO CALL DEP TO SEE IF THEY WERE SPOTTING THE LIGHT PLANE ON THEIR RADAR WHEN I REALIZED I WAS NOT YET SWITCHED OVER TO DEP FROM TWR. I SWITCHED AND CALLED THEM AND THEY SAID THEY HAD BEEN TRYING TO CALL ME BECAUSE OF THE ACFT. NEITHER MY FO NOR MYSELF HEARD THE SWITCHOVER REQUEST. I DID NOTICE STATIC IN MY HEADSET WHEN TALKING TO APCH CTL; SO MAYBE THAT WAS THE PROB FOR NOT HEARING THE SWITCHOVER FROM TWR. AT ANY RATE; I THOUGHT; EVEN THOUGH I SAW THE TFC AND DID NOT FEEL THREATENED UNNECESSARILY; IT'S A STRANGE PLACE FOR A LIGHT PLANE TO BE WITH A STEADY STREAM OF COMMERCIAL JET DEPS FROM THE PARALLEL RWYS 28 IN PROGRESS. HE APPEARED EXACTLY AT 3000 FT OVER THE SHORELINE WHICH WAS APPROX THE ALT A HVY JET DEPARTING SFO WOULD BE AT THAT POINT. ALSO; 3000 FT PUTS HIM IN THE TCA. IF HE WAS NOT CLRED; HE WAS CLRLY VIOLATING THE TCA. IF HE WAS CLRED; I WOULD QUESTION THE WISDOM OF ALLOWING HIM THERE FOR JUST THE REASON THAT UNFOLDED. ACFT DEPARTING SFO MUST CHANGE FREQ FROM TWR TO DEP CTL IN A VERY SHORT PERIOD OF TIME. THERE IS SIMPLY TOO MUCH GOING ON IN THE COCKPIT DURING A TKOF; A HIGHLY CRITICAL PHASE OF FLT; TO COUNT ON THAT CHANGE GOING SMOOTHLY EVERY TIME.