Here's a snippet from an interview with veteran New York literary agent Nat Sobel, which had me nodding agreement vigorously:
"I think what is evolving today for agents is that they need to be the first line editors for their authors. Judith and I really love the editing process. We have spent years editing nearly every novel we've ever agented. We did that long before we began to discover how little editing was going on in the publishing houses. But today agents need to be far more proactive in almost every other area of the publishing process. We have to be the marketing directors for many of our books. We have to involve ourselves in looking at the jacket design, the jacket copy, the catalogue copy. We have to be very proactive in how we help direct the writer to help sell his or her book. Those are things you never thought about in agenting when I first came into it. You made the deal, you negotiated the contract, and that was it—the publisher took over."
Editors involve me in all areas of the book. They can't build a little walled fiefdom in which agents are not welcome in the 21st century, though some try. The agent in 2008 must have an overview of all aspects leading up to and on through publication of his or her clients' books.
The whole interview is here, and makes fascinating reading:
http://pw.org/content/agents_amp_editors_qampa_agent_nat_sobel