I sometimes wish job hunting was more like submitting a book.
You see, with an interview, you submit your resume and application (usually online) and you wait weeks… months… with no word. Meanwhile, you chuck out another dozen to two dozen resumes amongst other companies and hope for the best. Eventually you hear back from one or more and you begin the next step in the process of being hired.
Meanwhile, a publisher or agent will usually let you know very quickly whether or not they are interested in your work. If they are, they ask for more. Or, better still, mail you a contract. However, most publishers and agents prefer you not submit to anyone else while you’re submitting your work to them, which begs the very simple question:
Why?
Why would any agent or publisher fear a dual submission? It’s not as though many new authors are going to have a bidding war break out for their book (if they do, more power to ’em).
My theory is simple: it’s easier to know, for an agent or publisher, that this author really wants only them. Is it ego stroking or good business sense?
What do you think?
Jason Córdova 
I’d say most publishers and agents assume you’ve queried widely. If they request your manuscript it’s possible they’ll ask for exclusivity while they consider your work.
I don’t know… most agents and publishers I’ve dealt with mention in their submissions guidelines that they don’t like multiple submissions amongst different publishers.
Granted, if they say that and then assume you’re going to ignore it, then what’s that say about expectations and following instructions?