This is a somewhat tongue-in-cheek top ten list that I originally did for talk.oringins a couple of years ago.  I just found it again and it seems appropriate for this group as well.

1. It allows for a more powerful and smarter God.  On the one hand you have a God who individually and lovingly crafts every portion of the creation, including each plant and animal species and man.  This is indeed impressive and it does appeal to me because it makes me a special creation of God.  But how much more impressive is the God who could automate the whole process, creating a self-sustaining universe, a universe that developed over a period of nearly 14 billion years, a universe that is filled with an unimaginable diversity of life.  Inanimate life that includes galaxies and stars as well the plant and animal life on this planet.  How much more worthy of honor is that God?
2. God is not deceitful.  If the universe was created in a complete state 6-10 thousand years ago, how can the appearance of age be accounted for?  Did God plant it to make the earth and universe look old?  To me, this smacks of deceit.  Especially evidence that would seem to be designed to throw people off the trail.  If God is planting evidence, how could we ever really know and understand his creation?
3. Allows the Bible to be what it is intended to be.  In 2 Timothy 3:16-17 Paul said that the purpose of the scriptures is to train me in righteousness, helping me to grow in maturity as a believer.  Nowhere does the Bible imply that it is a book of science.  It does indeed tell us that God created the universe and does give a brief outline.  But it does not tell us how it happened.  The purpose of the Bible is to help me to know God better and to better serve him, not to give me details on how the earth functions (see #4 below).
4. Allows science to do what it does best.  Science is about discovering and understanding the natural world.  Science is not anti-God nor is it pro-God.  It should not be expected to confirm or deny anything that is supernatural.  Science helps me to understand this universe that God has created.
5. The scientific evidence demands it.  The overwhelming evidence across physics, cosmology, chemistry and biology is that the universe is very old, that the earth is very old and that life on the earth is highly related.  The only science that supports a young earth or a special creation of man is done by people who are operating from a need to use science to prove a specific theological point. 
6. Allows me to avoid convoluted explanations about the physical evidence.  I don’t have to distort the findings of geology to support a young earth.  I don’t have to hold to untenable positions while explaining the similarities in different species today.  I don’t have to avoid mainstream scientific explanations for how things work.  I do not have to reject the finding of science because I find them disagreeable.
7. It provides a rationale explanation for earthquakes and cancer.  If God has created a self sustaining universe, proving all of the necessary raw materials and tools (natural laws and process) to allow it to develop and function.  And if this planet then developed enough for life to form and evolve on it.  And if God allowed that to occur in a hands off fashion.  Then how can we blame him for earthquakes and hurricanes and other natural disasters.  They are just a part of the way the world had developed.  The same is true for all of the diseases and other physical ailments that afflict us.  We have evolved into a highly developed although not necessarily optimized form.  And at the same time we have been involved in an arms race with a bunch of other little critters that prey on us.  Some folks might be upset that God does not stop some of these things from occurring.  But that is different than blaming him for them.
8. Allows Christians to engage their society without getting hung up on unimportant and irrelevant things.  As a Christian I am called to make a difference in people’s lives.  But that is very hard to do if I am instead fighting over stupid things that don’t really matter.  I end up being irrelevant.
9. I find it amusing to periodically be called an atheist. 
10. I don’t have to argue with our resident scientists about DNA.