Yes, that's what I thought I would do. If the user is logged in, it definitely makes sense to track by username.
Should I also include cookies as an option (for guests)? I.e. track according to cookie and/or ip (maybe even forbid voting for a certain amount of time)?
Should the default permissions be rather relaxed or very restricted?
As for permissions for writing polls and for voting, they will be related to the value of $USER->{user_forum_permission} (or of $GUEST->... for guests). This means that you can choose which minimum permission (in a specific forum) a user/guest has to have to make an new poll/vote.
E.g. you can set the permissions in such a way that only moderators of a forum can write new polls, and only users who can post a new thread can vote. Or you could set them in such a way that everybody who can post can also make a new poll, and everybody who is allowed to view the posts can vote. I think it should be flexible enough in this way.
Ivan
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Iyengar Yoga Resources / GT Plugins