I am interested in learning how other people use Priorities and Dates in their own RTM systems. Please share how you use them, and what other elements may be integrated.

Here's what I do:

Priorities 1 & 2 are both MUST COMPLETE items.
Priority 1 indicates that the Due Date is a hard deadline and cannot be changed unless the deadline changes.
Priority 2 indicates that the Due Date is not a hard deadline and can be adjusted as needed.

Here are the Priority and Date rules I've setup for myself for my RTM system:

Priority and Due Date
• P1 – MUST complete, has a set deadline (mandatory start/due dates; due date = deadline)
• P2 – MUST complete, has no set deadline (mandatory start/due dates; set/change due date as required)
• P3 – WANT to complete (optional start/due dates)
• P4 – MAY complete someday (optional start/due dates, but usually none)

As I'm always looking for ways to improve my system, I'd love to hear how others use Priorities and Dates.