A few words about Literary Agents. First and foremost, the disclaimer: The opinion about to be expressed here is mine, and only mine, and should not be taken as an absolute. It is up to the individual who is serious about being published, to decided whether or not that they should get an agent.
My first and only agent, The Eaton Literary Agency, I found through a contest that they had listed in the Novel & Short Story Writer's Market reference book (highly recommended). I had submitted my manuscript to them and about several months (and about $5,000) later, I had a "viable" manuscript ready for submission.
In November 2007, after being with them for about 17 months, I terminated my contract and took back my manuscript. I then began what eventually turned out to be, a fruitless search for another agent.
My experiences with trying to land another agent, brought me to this conclusion: most agents are afraid to take risks and prefer the status quo when dealing with publishers. Even though in their listings that they have (Guide to Literary Agents was the only one I used. Highly recommended if you're trying to land an agent for your manuscript or movie/television script), they say that a percentage of their clients are new/unpublished, it seems to me that they really want someone else to do their work for them.
As in, let someone else take a chance on publishing this "writer". If they get published, then we'll take a look see at them. Otherwise, it's a "don't call us, will call you" kind of attitude. I can truthfully say that the only rejections that I got, that I really respected, were the ones who actually read my material (synopsis/sample chapters) before rejecting them. The ones that rejected me, just based on my query letters, I had no respect for.
I still don't have complete respect for literary agents. I compared them to being a flock of sheep, with their sheep dog being the next big literary hit, herding them from ranch to ranch, desperately trying to find that golden egg.
Agents don't live in the real world. They live in a fantasy world of their own making. If they actually knew what the buying public really liked, they would take more chances with new and unpublished writers.