When user is deleted, his/her poll votes are not removed (which is kinda confusing, especially when you opt to remove even user's posts). Even more, manual deletion of the vote does not affect the vote count, which needs to be manually modified as well. This is very inconvenient when one user tries to tamper with poll results by creating fake accounts to vote - you need to delete all fake users, then manually delete all their votes, then manually update votes count. (I know this particular situation can be circumvented by limiting permissions to new members, but if it already happened, it would be good to be able to repair the damage done to a poll without manually fixing data in SQL tables).
I'd suggest an option\button in ACP to "resync" all polls on conference, deleting votes from deleted users and then updating vote counts. It would be very handy.