The idea of an agent sounds fantastically attractive to me for the next time I'm job hunting and looking to break in to a new area/field/whatever. It's work, and it's not the sort I enjoy, so yeah, I'd be willing to pay for it.

Also, the idea of having an agent to negotiate salary, at least initially, sounds great since the agent will presumably have a lot more knowledge of other salaries in the area or even at that company and the information situation would be more balanced.