How can I go about getting users to join groups by checking a box in a custom field? For example, my website deals with gamers. I want people who are primarily ps3 players to be able to click a "PS3" checkbox and automatically be put into a group. I did this with ProBoards before, but have no clue how to go about it with Xenforo.
So, i've been experimenting for a while. And it looks like the method you've mentioned @Brogan works for new members who join, but it doesn't seem to work for existing members who are already a part of the forum.
Okay, I see now. It is joining them to the group. But I have the usernames styled to be a certain color for a certain groups. And for some reason that doesn't change unless I re-save their profile settings through the Admin Panel. Weird.