As of June 30, 2011 there were 3,369,548 documents available as free full text through PubMedCentral, as compared with 3,285,816 on March 31, 2011, an increase of 83,732 free documents this quarter.
There were a total of 91 days this quarter; at 60 minutes per hour and 24 hours per day, that's 131,040 hours altogether. 83,732 is .64 of 131,040.
This means that PMC is adding free documents at a rate of 2/3 of a document per minute, or, rounding up, approximately one document per minute. Thanks to the Linked Science Workshop organizers for pointing out this phenomenal growth rate of PMC, hereby supported mathematically; this fact certainly belongs in the Dramatic Growth of Open Access series.