The frequent accusation:
Various scientists have challenged William Dembski's work, and claim that he hasn't provided enough research to fully answer their objections.
Here is a good source for Dembski's response to those critics.
Like ID, evolution also has unanswered questions, yet we don't thrown the baby out with the bathwater. Just because we don't know, doesn't mean we won't know...and that can be applied to Intelligent Design as well as the Theory of Evolution.
Here is another link in regard to Dembski's latest book, No Free Lunch: Why Specified Complexity Cannot Be Purchased without Intelligence.