IMMEDIATELY AFTER A NIGHT TAKEOFF IN FOGGY CONDITIONS, THE AIRPLANE IMPACTED TREES 1560 FT FROM THE DEPARTURE END OF THE RUNWAY. WITNESSES REPORTED THE ENGINES SOUNDED NORMAL & 'IN SYNC.' THE LANDING GEAR WAS RETRACTED. THE VISIBILITY WAS ESTIMATED TO BE 1/2 MI WITH PATCHY GROUND FOG. THE PILOT'S LOGBOOK SHOWED 3 FLIGHTS IN A PIPER PA-23 DURING 1990 FOR A TOTAL TIME OF 5.5 HRS, THE LAST OF WHICH WAS IN JUNE OF 1990. HOWEVER, THE PILOT RECEIVED A 1-HR FAMILIARIZATION FLIGHT IN THE AIRPLANE 3 DAYS BEFORE THE ACCIDENT.