I'm using RTM as part of my GTD hybrid system for over half an year and this is what I came up with (at least for now):
1. keep it simple - I've got only "tasks", "waiting", "someday" lists
2. two smart lists
* @home (for personal tasks) - not location:office and list:tasks and not dueAfter: "two weeks from today"
* @work (for work/office tasks) - location:office and list:tasks and not dueAfter: "two weeks from today"
This ensures that any task goes in one of the two smart list - you do not want to miss something!
3. mark tasks releated with projects prefixes like "TRAINING: ...task description " - I've found it quite complex to deal with projects using tags, which contradict to my KISS philosophy. Everything else that is projects related stays on my spiral notebook :-)

The only drawback of RTM with this simple setup is that it is always overloaded with tasks. There are so many of them, that I can easy miss something. For example usually I have around 30-40 next action tasks in @home, and 50-60 in @work lists. Of course there are the deadlines (due date) and the priorities to fix this, but still this means that all 2/3/4 priority tasks are just forgotten way down on the list.

So at the end I've came up with one additional smart list:
"today" - due:today or tag:today

That way I instantly see *ONLY* the due today tasks and I can easily add tasks to that list by tagging them with "today"

So with this smart list, I spare 10min to go through the lists and see what I would like to mark with "today" (as you do it only once per day its harder to miss something) and during the rest of the day I'm "looking" at a list that is only 5-10 tasks long - much better!