Here is a thread about whether to self-book or to use an agent:
http://www.flyertalk.com/forum/Forum94/HTML/003350.html

With the recent Consumer Reports Travel Letter article showing that travel agents rarely provided the lowest fare even when asked, you have to ask: What purpose does an agent serve today?

I suppose they're useful for complicated overseas trips and cruises, but not for point-to-point domestic air trips.