Managing Editor of PLoS One, Peter Binfield, recently published a paper entitled "PLoS One: background, future development, and article-level metrics"in which he outlines some of the recent upgrades at PLoS One and future plans for article-level metrics.
What Pete also mentioned in the article is the doubling in articles published every year:

• 2007: 1,231 articles
• 2008: 2,722 articles
• 2009: ~4,300 articles
• 2010: ~1% of PubMed?

If this trend indeed continues until 2010, PLoS One will be the largest journal on the planet, if measured by number of articles published (PubMed lists thousands of journals). Today, PLoS One already has more than 800 Academic Editors (I'm one of them) donating their time for handling peer-review and 30,000 authors have published with PLoS One.
I wonder whether this growth is just siphoning off excess publication pressure, or if some smaller journals are already seeing their submission numbers decrease. I take this growth also as a sign that people are fed up with our publishing system and embrace a publishing venue where they know they will get published if only their sience is sound.