CESSNA 172, N29150, & PIPER PA-28, N8465Y, WERE BOTH DEPARTING FROM A PVT, UNCTLD ARPT AT THE SAME TIME, BUT FROM OPPOSITE DRCTNS ON THE SAME RWY. THE RWY WAS CROWNED IN THE CENTER WHICH PREVENTED LINE-OF-SIGHT TO ACFT ON OPPOSITE ENDS. EACH PLT STATED THAT HE MADE THE APPROPRIATE RADIO CALLS ON THE UNICOM FREQ BFR STARTING TKOF. DRG THEIR TKOF ROLLS, THEY APCHD EACH OTHER NEAR THE MID PART OF THE RWY. THE CESSNA PLT STATED HE MNVRD TO THE RGT WHILE THE PIPER REMAINED IN THE CENTER OF THE RWY. THE PIPER PLT STATED HE SWERVED RIGHT, BUT THAT THE CESSNA WENT LFT, THEN RGT, THEN LFT AGAIN, & FINALLY HE PULLED UP TO AVOID A COLLISION. AS THE ACFT PASSED, THE LFT WING TIPS COLLIDED. THE OCCUPANTS OF THE PIPER HAD 32 BAGS OF MARIJUANA IN THEIR POSSESSION. THE CESSNA PLT, AN MD, STATED THE PIPER PLT HAD DILATED PUPILS, FACIAL SWEATING, TREMULOUS HANDS, TELEGRAPHED SPEECH, DIAPHORETIC APPEARANCE & SHOWED GENERAL AGGITATION.