I like PLOS. I really do. Look I've published two articles with them. I fully believe that they represent a big stepping stone to the future of science publishing.

Yet, oh yet, I feel like their attempt at building community is kinda shoddy at the moment. The heart of any social media website (reddit, slashdot, 4chan etc.) is the commenting and rating system. The commenting and rating system of the PLOS website is really poor, and I can't see how it will gain traction given the usability failings.

1. Log-in is too complicated. You actually have to go to a separate page. The rest of the site uses javascript, why can't the log-in? Most major sites just have some fields on that you fill in. From usability studies, the biggest obstacles are the simplest ones at the beginning, such as extra clicks for log-in.
2. The ranking of articles, though admirable, is unusable. I know PLOS wants to be the Amazon of science. But until you have Amazon's user base, don't try to have a rating system even more complicated than Amazon. For usability, the rating system should be considerably easier that Amazon, and less like a D&D character sheet. One three star rating, comes to mind, with no categories. This helps you avoid choice paralysis. But really, if you want to really exploit social media, you should have only two choices: like/dislike, and let the aggregation of the users make an article significant or not. That would be truly embracing social media.
3. The comments page is horrible. The way the comments are separated from the article suggests that the editors have no real faith in social media, separating the anarchy of commenting from the sober peer-reviewed content. Well the way they've got it set up, it's unlikely they'll ever get enough people commenting to have any problems whatsoever.

The comments are not integral to the article. There is a hermetic seal between the comments from the article by the fact you need to make two clicks from the article page before you see even one comment. No one will ever discover comments by accident. Discoverability is inversely related to the number of links to the information.

The comment page is a mess. Whoever designed it must have used an off-the-shelf forum commenting system. All sorts of metadata are included making the comment itself the smallest and faintest font on the page. The comments are not actually shown on the first comment page, just the comment headers. If you're pumping out hundreds of comments a day, this might be acceptable, but since it's a dribble, it's ridiculous that there is more screen-space devoted to comment headers and comment meta-data than the comments. In top commenting websites, such as Reddit, you are shown all the comments, and there is no need for headers, which are not only a waste of time but another usability obstacle.

Even worse, if you want to post a message, you need to click again! That's 3 clicks from the article, virtually burying the feature in web 2.0 terms. Most community websites have a text-entry html box at the bottom of the page, often using javascript to give it a nice interactive experience. Since PLOS uses some nice javascript in other parts of the site, it's not the technology that's the failing, but the lack of vision.

In short, it is prohibitively expensive to add comments, and when the comments are posted, they are displayed out of context and difficult to read.

If I may as be bold as to make some suggestions, then

1. Add login and password fields to every page. Make it ridiculously easy to enter the system as a participant.
2. Change the rating system to either just three stars or like/dislike
3. Add a popular article page where articles are actively ranked by a combination of the rating and page views.
4. Make an abstract page where the comments are shown directly below the abstract.
5. Show the comments like reddit.com – no comment heading, all comments threaded below the abstract, minimal meta-data, so that all you see is beautiful comments.
6. Stick a text-entry box at the end of the comments to invite new ones.

So, please PLOS, I think you're great, but you could be greater still, you might even be the first open-access site that truly embraces social media.