The issue of publishing first rights is one that causes paranoia among many who post on internet forums. The belief that work may not be accepted if it has first been shown on a blog or writing site is one of the greatest modern myths. The only time this appears to be a real issue for poetry and short stories is with some of the newer e-zines that have appeared over the last few years. With novels it's more relevant but even then publishers don't raise an objection if extracts have been shared because it can help with the promotion of the finished product. I have never found that having poetry or short stories published on the web has been a block to getting published elsewhere. With poetry specifically, I tend to remove much of my work from the web after a period because people aren't going to pay for something if they can get it for free. Even so, I usually leave a few works out there as a taster.
I only know two people personally that have been published and both of them posted their stories online chapter by chapter and had people review, read, and feedback. One is a literary agent, so he sort of already has his foot in the door. The other had many, many other stories up that she posted online before she was able to get published. While I agree that having a story up is not an automatic reject - I still rather be safe than sorry.
I know of three people who have their first book published by the traditional route within the last two months. All three posted parts of their work on internet forums for critique before sending the finished product off to agents or publishers. The fact that they had put their works through internet workshops prior to submission was no barrier. I can name those writers and provide links but that would probably be in breach of this site's spamming rules. I think it's great when I see other writers I've known from the forums getting publishing deals and it's even better to know that the forums have helped them get there.
It's not necessarily "better to be safe than sorry" if you can gain something by posting your work online, like promotion.
