GRAND PRIZE WINNER:

When a cat is dropped, it always lands on its feet, and when toast 
is dropped, it always lands with the buttered side facing down.  I
propose to strap buttered toast to the back of a cat; the two will
hover, spinning inches above the ground.  With a giant buttered cat array, 
igh-speed monorail could easily link New York with Chicago.

RUNNERS-UP:

#1
If an infinite number of rednecks riding in an infinite number of
pickup trucks fire an infinite number of shotgun rounds at an
infinite number of highway signs, they will eventually produce all 
the world's great literary works in Braille.

#2
Why Yawning is Contagious:  You yawn to equalize the pressure on 
your eardrums.  This pressure change outside your eardrums unbalances 
other people's ear pressures, so they must yawn to even it out.

#3
Communist China is technologically underdeveloped because they have 
no alphabet and therefore cannot use acronyms to communicate ideas at 
faster rate.

#4
The earth may spin faster on its axis due to deforestation.
Just as a figure skater's rate of spin increases when the arms are
brought close to the body, the cutting of tall trees may cause our
planet to spin dangerously fast.

HONORABLE MENTIONS:

#1
Birds take off at sunrise. On the opposite side of the world, they
are landing at sunset.  This causes the earth to spin on its axis.

#2
The reason hot-rod owners raise the backs of their cars is that 
it's easier to go faster when you're always going downhill.

#3
The quantity of constants in the English language is constant.  If
omitted in one place, they turn up in another.  When a Bostonian
"pahks" his "cah", the lost r's migrate southwest, causing a
Texan to "warsh" his car and invest in "erl wells."