I ran across a great video of Os Guinness speaking at the Trinity Law School God and Governing Conference in February 2008. While his topic was on sustaining freedom in our nation, in his introduction he related what he thought were the results of evangelical overemphasis on political activism:
When we consider the state of both the church and our nation today, I believe he has a point.
Other messages at the conference dealt with this issue further. I hope they might be available soon.