O.K. I'll let you know a couple
reletively minor ones.
If you read the FARs (Federal Aviation Regulations), control cables are to be routed in specific types of ways. One way is that the cable can not ride along a surface causing a deflection of more than 3 degrees of the cable. This is to ensure that the cables don't wear or work harden. The Piper Cub series has 2 very obvious 20 to 25 degree deflections of it's aileron cables.

Here is another:
Piston engine aircraft engines, according to the FARs, are to have means for reduntent ignition systems. This is why there are two [b]independent[b] magnetos on your engines, if one fails (weather it is the gearing, the drive mechinism or just the points/contacts), the engine will still run so you can safely fly to an airport. One magneto manufacturer and engine manufacturer decided that 2 magnetos cost too much, and complicated the eninge. So what they did was setup a dual-magneto system that ran off of a common drive. If that drive fails (or the gear) both magnetos will be rendered useless, and the engine will stop. Not exactly good, cause then the pilot would overheat, since the propeller is the big fan that keeps the pilot cool. If it stops, he gets all sweaty.
Then there are simple things that peak interests, such as:
The Boeing 707's rudder is not controlled directly. It is actually controlled by the trim tab. The control yoke only controls the trim tab, which will move the rudder side for control. The rudder is free floating, so back in the early days, passengers would get worried seeing the rudder swing side to side while at the gates due to the winds. So Boeing made a modification that would lock the rudder in place when the aircraft was taxiing and parked. If you want to see them still do this, look at the military varients of the 707, they don't have this modification, and the tails still swing in the wind.
Maybe I should start a thread about interesting aviation facts? Post a new interesting fact every week or so? Whaddya think? I have some interesting and freaky things to say, but I don't want to put out false information without double-checking myself.