Einstein's theory of relativity, the quantum theory of physics, and the Copernican theory that the earth revolves around the sun are scientific theories. The theory that the line you get into in the supermarket always takes the most time, or that the best way to make it rain is to get your car washed, or that right when you sit down to dinner, the phone will ring may all fit into one of the definitions of "theory" that you'll find in your dictionary — such as conjecture or supposition. But like "intelligent design," they just don't happen to be scientific theories.
Intelligent design promotes the idea that an unseen force is behind the development of the Earth and humanity. Those who embrace intelligent design don't like to say that they believe the "unseen force" was God. I guess they feel it won't sound scientific. To me, trying to make a spiritual idea scientific undermines both the spiritual idea and science. It's sad that religious people should feel afraid to admit that they feel God was responsible for creation.