There are download stats for dmd, the reference compiler[1]. Anyone doing production work is probably using gdc or ldc though so that's not the whole picture.

They have an orgs using D page: https://dlang.org/orgs-using-d.html

If you look at the various language rankings (taken with a mountain of salt) D is still fairly low overall. Definitely one of the higher languages without a corporate/industry backer though.

1. http://erdani.com/d/downloads.daily.png