PLOS, the Public Library of Science is by many measures a great success. Contrary to naysayers its online journals are well-respected and often cited (which is the real measure of currency in academic research).

Their latest announced project is PLOS One, a "forum" for publication in science and medicine. The nearest I can do to summing up the proposal is that it looks like a peer-reviewed collaboratively authored science blog. Obvious competitors are general purpose high-quality online science publications such as Scientific American, but these have heavy editorial control and limits. It will be interesting to see if the author-driven model can succeed as well as PLOS's more traditional journals have.