The following graph shows the monthly download figures of the PDF version at http://ddili.org/ders/d.en/index.html

  http://ddili.org/Programming_in_D_monthly_downloads.svg

Regarding just December 2016, there are also the following figures:

  EPUB version downloads: 115
  AZW3 version downloads:  50

Highest page visits for the HTML version:

  /ders/d.en/                   2,290
  /ders/d.en/hello_world.html     235
  /ders/d.en/ranges.html          208
  /ders/d.en/arrays.html          136
  /ders/d.en/types.html           133
  /ders/d.en/foreword2.html       131
  /ders/d.en/assignment.html      130
  /ders/d.en/compiler.html        129
etc.

Ali