There are more YEC then OEC these days beacuse of how science is progressing. We are learning more and more about entropy and how energy decreases over time in a closed system. New theories about comets and studies on Quantum Mechanics are leading more to the YEC as well.
Based on what I know I see the following facts leading to YEC
The Genesis account states that there was a definate beginning and end to creation. This would mean that since God is omniscient and was here before creation, that he must exist outside of time and space.
So although there was a definant start and finish to the creation process, God was able to create it from outside of the constraints. After every creation day it says "the evening and the morning were the next day". Evening and morning result in one day for us, but not for God.
"And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day."
In addition, man was created on the 6th day. If God rested for thousands of years on day 7 then this would have posed a problem for Adam, and definately for the Animals. We are not lead to believe that Adam was thousands or millions of years old when Cain and Able were born.
For these and other reasons I will not get into now, I stick by the idea that God created the World "In motion" in 6 literal Earth days which ultimately mean nothing to God. See the differences in these verses.
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
And God said, Let the waters under the heaven be gathered together unto one place, and let the dry [land] appear: and it was so.
God speaks the earth, water and sky into existence, the waters above the earth are said to be what protected man from the sun, and ultimately flooded the earth killing everyone but Noah, and causing post flood man to live shorter lives because this protection was gone.
And God said, Let the earth bring forth grass, the herb yielding seed, [and] the fruit tree yielding fruit after his kind, whose seed [is] in itself, upon the earth: and it was so.
And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl [that] may fly above the earth in the open firmament of heaven.
And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so.
In these verses the water and earth are bringing forth life. This is the start of the Micorevolutionary process and the reason why so many scientists are lead to believe the earth is millions of years old. In order for God to have the Earth and water bring forth life, there had to be immediate conditions suitable for it. So God spoke into existence "In motion", meaning that they did not form over millions of years from a Blast of energy, they were simply there in full form.
Of course there is much debate over this issue, and not something that Christians divide over, but it makes for great discussion and debate.