I'm tired by all the bugs reported by newbies who know nothing about our triage process and which file their bugs with priority P1 just to have them at the top of our TODO list. I know it's enough to turn off the letsubmitterchoosepriority parameter to prevent that, but I cannot imagine any real use case where it makes sense to let someone with no privileges decides what the right priority is. Either the guy knows what he is talking about and he has the rights (aka editbugs privs) to edit the priority field, or he shouldn't be allowed to play with it. If the reporter thinks his bug is important, he already can set the severity field when reporting the bug. So I suggest to remove the letsubmitterchoosepriority parameter entirely, and hardcode it to 0 everywhere where it appears.
letsubmitterchoosepriority is very much a per-install decision; i don't think it's reasonable to enforce usage pattern for this field onto all bugzilla installations. i've worked in corporate environments where the priority field is largely used correctly by reporters -- with the priority being the importance to the reporter, and the severity being the triaged level. with respect to larger open systems (such as bmo), different products have different triage processes; perhaps it would make more sense for this setting to be configurable at a per-product level rather than globally?