Most every computer science conference has (at least) two rates for registration: students and other. Ostensibly, this is because we want to encourage student attendance at conferences. While it's not often put in these terms, it should be said that this is part of the reason registration fees seem so high: non-students are effectively subsidizing students. (Which, I think, is fine.)
What about post-docs? I've had this question in the past when I was running local arrangements for a conference and have unsurprisingly heard it come up again recently.
I've looked around and, as far as I can tell, separate registration rates for post-docs don't appear common. I don't think any of the conferences I regularly participate in have them. If you know of conferences that do, please comment.
Since CS seems increasingly to be moving to a state where postdocs will be common -- possibly the norm -- this seems to be a question worth considering. The problem is there is a big range in postdocs. We'd like to charge postdocs with money (such as, say, postdocs in research labs that pay for conference travel) the full rate to keep standard registration rates low, but we'd like to charge postdocs that don't have specific travel money less so as to encourage their attendance (and not burden them financially). While it would be nice to have two different postdoc rates -- postdocs with money and postdocs without -- I don't think that would go over well with conference organizers or the people who could pay for postdocs.
The default we seem to have wandered into is that postdocs are charged the full rate, but I'm unconvinced that the system ended up that way because of careful thought. Perhaps it is because until recently postdocs have been relatively rare. It seems a question worth revisiting. Any opinions?