OK, so I've been working two jobs for two and a half years. And I've been doing a pretty good job of balancing the responsibilities of both.
I have four agents working for me, and a website (lperkinsagency.com) that gives writers a very detailed description of what we're all looking for. And I have personally stopped taking on new clients (unless, of course, Stephen King begs me), so I can focus on guiding my junior agents. We have broadened the scope of the agency as well. We have an ebook only agent who is kicking ass (and can really guide writers on that part of their careers) and we've starting selling children's books (Louise Fury just sold a children's picture book to Random House), not just young adult and middle grade fiction.
I go over every book that is submitted under my agency name with my junior agents. We do contracts together, so every contract gets my years of agenting expertise (and boilerplate). So I find it a little surprising that writers seem disappointed that I am no longer taking on new clients. Even if I wasn't running a publishing company (Ravenousromance.com now publishes about 200 books a year, and I personally edit 50 of them, and oversee a staff of five), I would probably only take on a handful of new clients a year. By running the agency and supervising, I (we) can launch many more new careers and resurrect old ones. The odds are actually much better for the unpublished writer here now.
But we are swamped. It staggers the imagination to see how many queries we get. An agent's life is not all about queries, especially now that it takes longer for editors to get approval on purchases (I have a book by a NY Times best selling author who has sold over 400,000 copies in hardcover that I have been waiting on an offer for for over 9 months), we can submit a finite amount. It makes no sense to have five horror first novels piled up with the same editor.