THE WEIGHT SHIFT CONTROLLED, ULTRALIGHT VEHICLE HAD JUST RECENTLY BEEN BUILT. THE OWNER & THE PLT HAD AGREED THAT THEY WOULD NOT ATTEMPT TO FLY THE VEHICLE ON THE INITIAL TEST. THE PLT WAS OBSERVED TAXIING EXCESSIVELY FAST, AND REPORTEDLY, HE MADE 1 OR 2 GROUND LOOPS WHILE TAXIING. AFTER HE TAXIED THE VEHICLE APRX 1/2 TO 1 HR, IT BECAME AIRBORNE. THE OWNER REPORTED THAT AFTER LIFT-OFF, THE VEHICLE LEVELED OUT AT ABOUT 50 AGL, THEN WENT ALMOST STRAIGHT UP TO APRX 100 TO 150 FT. IT THEN TURNED & ENTERED A DESCENT & CRASHED IN A NEARLY STRAIGHT-DOWN ATTITUDE. ANOTHER PLT HAD TEST FLOWN THE VEHICLE EARLIER IN THE DAY. HE REPORTED THAT THE CONTROLS RESPONDED NORMALLY. THE PLT THAT WAS INVOLVED IN THE ACCIDENT HAD A BALLOON RATING & WAS INDORSED FOR SOLO FLTS IN A CESSNA 172; HOWEVER, HE HAD NO PREVIOUS ULTRALIGHT EXPERIENCE.