There are problems with posting work online and then attempting to publish it (self-publishing not included as far as I know.)
When posting work on a non-password requiring forum that allows search engines to detect it, a simple Google search allows anyone to pick up your work. Many agents/editors/publishers will perform this search. And anything that's posted via the internet unless posted in a password protected area that cannot be picked up by a google search is technically 'published.'
Therefore, many publishers will not accept work that has already been posted on the internet.
There is a limit to the amount of work that can be posted online and still be accepted for publishing. I'm sure this amount varies among publishers, but a number I've heard somewhere is 10k words. Don't hold me to that number though. I can't remember where I read that.
http://absolutewrite.com/forums/showthr ... ?p=3677843
http://yzabel.wordpress.com/2005/10/08/ ... nt-rights/
However, others who even remotely think they might later want sell their NaNo novel (or anything else they’ve written) to a publisher, need to know that posting the story on an open site on the Internet is the same as publishing it. You have thrown away your First Print Rights, which are the ones that the publishers want.
Many people put their stories up on sites in the mistaken belief that if they aren’t paid for them, they aren’t published. This isn’t true. Anything that is in a position where it can be read by the public is considered published. This includes posting on your website, LiveJournal, Blog, or any site where just anyone passing through can read the work. It doesn’t matter how many people actually read the story, either.
Sites that are safe, however, are ones in which the reader needs a password in order to get to the story. Most writers’ sites with critique groups are set up in this way. ‘Friends Only’ LiveJournals are also safe because the owner has full control over who sees the posts.
There is some debate on the subject ion whether its unpublished or not, but to me it's better to be safe than sorry.
I'm sure the wonderful mods have considered this. But I wanted to say this anyway.
ETA: I'll continue to post links as I find them, but it's a little hard to find information on this.
http://editorialass.blogspot.com/2009/0 ... nline.html (Comments on this one are quite interesting as well)
Various opinions on subject: http://crimespace.ning.com/forum/topics ... mment27122
I need to find a recent, actual publisher's opinion...
