It's probably just moving the real lubricant that is there (factory grease)
into the friction area for a short period of time. Keep it up and you'll
wash every bit of real lube out of the hinge and wear it out. A real
lubricant shouldn't need to be applied more often then about every few
years. There are plenty of spray greases that thicken when they "dry" that
work much better for this sort of thing.

Actually I love people using WD-40 as a lube, I get to replace all the parts
that get worn out from doing this. It's about the worst lube or rust
penetrant of anything on the market today.

http://www.sandsmachine.com/grease_t.htm

He tested a bunch of greases, WD-40 was worse than the parts being used dry!

http://yarchive.net/chem/wd40.html

Explains it's basically something like kerosene with aprox 10%
oil/lubricant. It's a 50 year old formula that was designed to disperse
water and help prevent rust.

http://www.techshop1.com/tips.html

It's a really crappy lubricant for anything that has any sort of pressure,
like a door hinge.

Fill the oil pan of the engine with water and lets see how long it lasts.

The point was this "lubricant" doesn't have enough pressure resistance for
this application therefor it isn't acting as a lubricant for this
application. For something like a throtle cable it might be fine but for
anything with pressure on it, it's useless.