Is there any argument against the watchmaker argument other than asking for more rigor in the definition of design? So far, the argument strikes me as compelling on a common sense level -- but I admit I am predisposed towards it.
But the lack of rigor in defining "design" is precisely the problem. You can't claim that something looks designed until you define "designed"!
Let me construct a similar argument for you to show you what it looks like from our point of view.
=========
AfS: All life is sexy. Anything that is sexy could not have evolved. Therefore, life did not evolve.
CS: But how do you know that all life is sexy?
AfS: Why, that's obvious! I can name you many examples of life that are sexy. Madonna, for example. Keira Knightley. Wasps, with their wasps' waists. And crikey, aren't crocs -
CS: Well, if it's so obvious that life is sexy, then what is it about life that makes it sexy?
AfS: Well ... well - it's obvious! It's common sense that women are sexy! Do I need a
definition to convince you of that?
CS: Well if you can't define when something is sexy, then how can you know? Or maybe you can show me the difference between something sexy and something not?
AfS: Well, since all life is sexy, I naturally can't show you anything that isn't sexy.
CS: That's convenient. Or, even if all life is indeed sexy, how do you know that sexy things can't evolve?
AfS: Well, because evolution can't produce sexy things!
CS: What if I showed you that evolution can produce sexy things?
AfS: Well, evolution doesn't produce sexy things!
CS: How do you know that?
AfS: Because I told you that it can't!
CS: But I just showed you that it can!
AfS: That doesn't show that it did!
CS: How do you know that it didn't?
AfS: Why do I feel all dizzy?
CS: Because you've just made a circular logic pirouette. With practice they'll become so natural to you that you won't feel the slightest discomfort.
=========
If you haven't already guessed, AfS is the "Argument from Sexiness", and CS is "Christian Skepticism". While this doesn't capture all that the design argument is, I hope you will get how frustrating the vagueness of "design" is to people who genuinely want to engage your position. I personally have a definition of design which I'm happy with but which doesn't look good at all for design proponents.