I've been using e-mail for over a decade in a regular business environment, but I can not remember having seen any invitation from anybody to GPG sign my e-mails (or somebody who offered to send GPG-signed e-mails). Nevertheless, GPG appears to be the de-facto e-mail signing encryption mechanism.
So my question is: in what kind of environments have you seen GPG being used frequently? I'm thinking in specific industries, or perhaps only within companies where everybody has been trained and has their keys set up. But I'd like to hear from people who have actual experience with this. And is it useful to publish my key and put this in my signature, to see if other 'hidden' users will actually tell me that they also use GPG, or is this not very common among regular business users?