I'd like to be able to set one or more task reminders using an absolute date/time, not just relative to the due date. THIS IS PROBABLY THE THING I MOST STRUGGLE WITH USING GTD IN RTM.

In the GTD methodology, you are discouraged from putting a due date on your tasks, unless it really has a serious consequence for missing it (e.g.: file tax return - due April 15th), so MOST tasks won't have due dates - hence no reminders possible in RTM. I'm pretty good at managing my top-top priorities. I don't even need a task management system for them. It's the important-but-not-urgent things that I need to be able to log and feel good about having captured, but they can't slip forever. Ideally, I will notice these tasks in my weekly review, but in reality, I need to put a limit on how far I will let some things slip.

I tried using tags, but they became meaningless once there were more than 20 things in the list. Recently, I've been using the start date like a reminder, but that neutralizes the meaning of the start date!