Agents expect writers to submit to multiple agents at the same time. Unless otherwise stated on our agent sites, we allow for multiple submission.
But what about submitting to both agents and small/e-publishers at the same time?
There are so many conflicting opinions on this. I asked a couple agent friends and they all had a slightly different perspective.
Agents and small/e-pubs are apples and oranges. Agents will sub you to the bigger publishers, generally more money and more exposure, plus you get an agent advocate helping with contracts and helping guide your career. Small/e-pubs are generally less money and less exposure, but it can be a more intimate experience with editors working directly with you and they may have more time to concentrate on your career. Many authors are happier with small/e-pubs than they ever would have been with bigger pubs. But many authors aspire to the big pubs, seeing the smaller/e-pubs as a last resort. Some writers may not know what they want, just for someone to recognize them and tell them "yes" amid all the "no."
I, personally, suggest that all writers decide what they really want, the big press, or the small/e-pubs, and concentrate in that area. Imagine you get offers from both an agent and a small/e-pub at the same time. Now you have to decide what you really want--a chance at the "big time" or the sure thing and immediate publication? If your answer is "I'd take the agent offer," then concentrate on subbing to agents. If your answer is "I'd take the small/e-pub," then concentrate on those.
I understand the other side of the fence too. As a writer, you need to explore as many avenues as possible, and life is too short to spend so much time on only one opportunity.
So to sum up? I'm not personally of the opinion that you should submit to both, but I will not discriminate against you and the decision is wholly up to you (and many writers, agents, editors will encourage you to do both). My advice is merely to know what you want out of this business. There are so many options for you in this day and age, you need to educate yourself on all of the avenues and go after what you want--otherwise you're likely to get trampled in all the noise.
Has anyone had personal experience with this? What is your advice to other writers?