This will consist of two parts.
First, we can use the "who cares?" argument. Remember my post on the mass revelation argument? Its the same thing. Something that may or may not have happened a long time ago-- what relevance does it have for us? If life got here from evolution, so be it, and, perhaps we can learn from the biological principles how to possible better our lives now. And if life got here suddenly, when one day, the uncreated Yahweh went "poof!", so what? Who gives a flying f**k? Do the animals have to bow and express gratitude to their creater? Why should we? Since this Yahweh no longer seems to exist, perhaps he died or went to sleep, or moved on to something more fun. Who cares?
With regard to the watchmaker argument itself:
1. It is an analogy, the weakest form of argument. Since we know non-organic machines are man made, by analogy, life forms, with their apparent complexity and purposefulness, must have been created. But non-organic machines are different than life forms (we see that they replicate,, grow, change, evolve, which machines can't), therefore the analogy is invalid.
2. The analogy is powerful psychologically, because our brains are wired to see purpose and cause. When we see a watch, a priori we know it is a man made object. So we tend to attribute these elements of cause and purpose to all other entities that we see. By example, when ancient man saw lightening or thunder, he could easily argue that they were coming from the gods' anger, a very logical extrapolation from other human experiences. Loud noises and bright lights come from people or animals doing things. Yet when we learned that there is an alternate, non-creator explanation, we abandoned the gods explanation.
Can you guys come up with other powerful, succinct rebuttals?
[Bloggers note: sorry about the previous typos, I have made corrections to the post.]