For the record, I know the arguments behind Intelligent Design. It's based on philosophical postulations, scenarios, and ideas. Which does not make it an invalid theory in the least. It just makes it a philosophical theory, not a scientific one.

In order for a theory to be scientific, it must be:
A) Completely and utterly objective. That means that if an experiment is made, it must be recorded and carried out in a manner that can be repeated by any other scientist. In relation to theory, it means that "its laws and predictions are repeatable and unaffected by human preferences" [link]. That means that no outside source or influence other than the evidence and scientific knowledge should influence the theory.
B) Based on empirical evidence, meaning that the evidence that supports it is measurable and derived from experience and/or observation.

In addition to that, most commonly accepted scientific theories such as the Big Bang and Evolution have been tested via the link, which is as follows:

1) Question: Address the question/problem and set the parameters of your experiment.
2) Research: Look into previous answers/theories/suggestions and experiments. Set up your own experiment avoiding mistakes made in the past.
3) Hypothesis: Form a hypothesis you believe your experiment will validate in an easily measurable way.
4) Experiment: Conduct the experiment and carefully analyze the results.
5) Analyze and Reflect: What do your results suggest about your hypothesis? Did it answer your research question? As unbiasedly as possible, report your findings.

Intelligent Design is philosophical because instead of actual experiments it proposes "thought experiments," or that is to say creating a situation and logically deducing an outcome through philosophical reasoning. Like I said earlier, this is philosophy, not science.

I was thinking on how to exactly phrase why I don't think it is a science, but Cinders has done it for me. Thanks!

I think Cinders has pretty much said it all...

Of course everything I planned to say is already covered by Cinders... and better phrased too :P

I'd like to add that I laughed out loud when I read this pick, no offense intended to those who picked 'yes'.

Uhm... yeah. Cinders said everything that was running through my mind.

Five comments: one by Cinders, four agreeing with her.
None that disagree.

Cinders, you rock!

It's a religious theory, not a scientific one. Pretty much what Cinders said.