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.