As far as I can tell Intelligent Design was invented to explain evolution when it became clear to all but the most fundamentalist nuts that evolution was a fact. I think that if you suggested intelligent design 250 years ago the church would have had you executed as a heretic.
Intelligent Design is just a re-branding of Biblical young-earth creationism. It was devised by a team of lawyers at the Discovery Institute specifically to get around the American Constitution, specifically, the establishment clause of the first amendment.
It was de-bunked at a trial in Dover Pennsylvania in 2005. Here's the wiki link if you want to read the whole story. Dover Trial
As of 2008 a Gallup poll indicated that 36% of US adults agreed with the statement "human beings developed over millions of years from less advanced forms of life, but God guided this process.", 14% believed that "Human beings have developed over millions of years from less advanced forms of life, but God had no part in this process." and 44% of US adults agreed with the statement "God created human beings pretty much in their present form at one time within the last 10,000 years or so
It amazes me that 44% of the people in the self-proclaimed greatest country on Earth believe this. What scares me most is how much Britain seems to follow America. I hope this attitude does not gain acceptance over here.