Not many people do, which for someone who's obsessed with the industry, comes off as simultaneously wallbanger-worthy and hilarious. Wallbanger because all the kids these days are like, "I KAN GET PRINTED EASILY AND BE FAMUS JUST LIKE SMEYER AND PAOLINI LOLOLOLOL." And then, they run around, thinking they know everything about writing. Meanwhile, I'm sitting there thinking, "Yeah. Right. You know most major publishing companies' receptionists will toss your story in the bin if it isn't a perfect manuscript pre-screened by a literary agent, right?"
Then, I hear about the kids who actually try to send their manuscripts to anything other than a self-publisher or a vanity press, and I just laugh a little harder.
For those of you who are really, really curious about how it actually works, this is the sending process that's most recommended to do to avoid getting laughed at by, say, Macmillan or Random House and their million and one subsidiaries:
1. Remember that most publishing houses put out less than 100000 titles a year. Most of these titles are actually nonfiction. Subsequently switch to being a nonfiction author.
2. Finish your manuscript and proofread it carefully for plot, characterization, and language errors. Unless you publish through vanity presses (which publish anything) or self-publish on places like Lulu (which are neither cheap nor something many people take seriously) or sleep with someone in the company (which I believe is the only way Twilight happened), you're not going to get published with a subpar transcript.
3. Cover letters. They're not just for resumes, and you're not getting out of writing them. Know how to write them and what to include. Pimping your story is okay. Saying it's a hit before the agent decides is not. Not doing your research about the agent/company and failing to mention anything about them in the letter is fail.
4. When you have your manuscript and cover letter (for the lit agent), send your manuscript, and all the other steps beyond this is out of your court. Read up on lit agents because a handful of them still accept paper submissions, whereas others only accept submissions through e-mail. In general, research lit agents. Lit agents are lawyers, so you could just get ripped off. Also, yes, lit agents are a good thing. They send your story to exactly the right companies (unlike n00b authors who send their pulp romance novels to sci-fi companies, for example), and they negotiate your contract with said company. They also pester you to finish other books, and they convince the company that your manuscript is worth looking at.
4a. ...Usually because lit agents have already looked it over and laughed at all the stupid ones.
5. There is not just one editor who looks at your manuscript. There's usually an entire line of them, starting with the editorial assistant, whose duties usually involve not only reading over transcripts that were sent to the company but also answering phone calls and writing memos. That's right. If you fail at this step, you were laughed at by the receptionist/secretary.
5a. This is, of course, not including the list of other types of editors your story goes through before it finally gets to the top, the one editor who actually decides whether or not your stuff is the material they're looking for in the company.
6. And then, your story gets shredded by copyeditors.
7. Did we mention that by now, it's been months since you sent in your transcript? Never mind the fact that it's probably been a good couple of years since you sat down and put the first word on the page or the couple of months that it'll take for this to actually get printed after it reaches the copyediting part.
8. Ah! Finally! You've reached the printing stage! Here's your check for $300, not including the tiny bit you get in royalties after your lit agent takes his percentage. Thank you and come again?
Now, I'm by no means discouraging people to become writers. In fact, there's exceptions to this process. (Paolini, for example.) And there's crap that slips through anyway. However, I'm just saying that, yeah, it's not a get-rich-quick industry, so you just have to keep that in mind and brace yourself for something that isn't easy. Have another job to fall back on, or you're going to be penniless for a long, long time.