This post really intrigued me for several reasons including the value of a person's time - sort of like optioning a script then never producing it. What do you think of a "waiting fee"?
As a person who is currently sitting at his contract job where he is getting paid to surf the Internet instead of doing work because the company he is hired on to seems to not have any work for him to do, I fully support a "waiting fee" (whoops, run on sentence rant).
Especially in a freelancer position, if a company is looking for a freelancer to help them, gives the freelancer the indication of such and then goes off for a week or two to look at other opportunities, they are completely forgetting that freelancers live off of the jobs that they get.
A reasonable waiting fee will make it easier on the freelancer. Sure, they may lose some business from those who don't want to agree, but otherwise, they'll get the work faster, as Dann said.