Having talked to a number of Wikimedia (Foundation) development teams in the past, two or three teams that do not primarily use Bugzilla but other tools often mentioned that anybody can change the "Priority" field in of bug reports, so that priorities might not reflect anymore what the team really plans to work on.
This does not mean that it is planned to introduce restrictions when it comes to setting/changing priorities of bug reports; I'd just like to drop some collected information here that might help evaluating later (if needed and wanted).
Upstream ticket: https://bugzilla.mozilla.org/show_bug.cgi?id=372017
General upstream recommendations:
http://www.bugzilla.org/docs/tip/en/html/cust-change-permissions.html using check_can_change_field()
RedHat patch (against an old Bugzilla 3.x version) globally based on group:
MeeGo extension (against Bugzilla 3.6; per product configurable priority change control group, Admin is able to configure which group is able to change priority of given product from product administration page):
http://gitorious.org/meego-bugzilla/priority-chgctl/commit/50f907c5319a9065b835ca5e3b5340808d9ba614 http://gitorious.org/meego-bugzilla/priority-chgctl/commit/ef35841f75dd1c4f74a6135fd196addb726e0e10 http://wiki.meego.com/MeeGo_Bugzilla_customization