There are a couple universal questions pre-published writers always ask:
1. How can I find out a publisher's submission requirements
2. I'm halfway done with my novel -- should I go ahead and submit a proposal?
Agent Terry Burns of Hartline Literary Agency (http://www.hartlineliterary.com ) addresses the changing nature of submission requirements in his blog. In the past, there has been a little more leeway as to whether or not your manuscript needed to be finished before you submitted a proposal. Granted, an editor or agent is usually going to require only 3 sample chapters or perhaps the first 50 pages, but they could also then request a full manuscript.
Mr. Burns recently surveyed industry professionals on this subject and you can view the results here: