I think we have to be even more aware especially with high costs of fuel and hard times.
A juicy fat twin with unsecured caps must be a target not just from external thieves but private owners feeling the pinch.
I flew a Seneca which was hangered although the hangar doors were open in the day. We were loosing fuel so started locking the fuel caps.
few days later came back to the aircraft and there were chips and scratch marks around the fuel caps where someone had tried to prize them off with a screwdriver.
There are obvious dangers of thinking you have X amount of fuel and next day taking off with X - ?
Also as another poster put beware of vandalism where some clever clogs decides to tip some water in the tanks or grinding paste into the oil filler or even worse tamper with the controls. There are many anti aviation nutters about!
Even more reason to do thorough pre flights especially first flight of the day!
Pace