At pMD we have access to a lot of interesting data. Through the pMD charge capture app, providers record detailed descriptions of their encounters with patients. This data not only facilitates billing and reimbursements for a practice, but also serves as critical communication between providers. Looking at this data, we can get a rough measure of the volume of patients seen by our doctors and mid-levels throughout an average week.
Looking at visit counts for two full years (2012 & 2013) and across all of our specialties around the country, we get the chart below:

So it looks like work slows down in sheer volume, but still more than 20% of patient encounters occur on the weekend, and most likely among fewer covering providers.