The demand for sub-tasks seems to be growing on these forums, so I thought I'd offer up my own personal sub-task system, to save others the trouble of experimenting with complex tagging systems and the like.

In the event that I have a major task on my to-do list, like "Clean the basement out", I would like to be able to use sub-tasks, like "Move the refrigerator out" and "Donate bags of clothing to the Salvation Army."

Here's how I've achieved this:

I create my "Clean the basement out" task
I create a new note for the "Clean the basement out" task
I list out the subtasks on the note, in their order of completion

The next time that I'm cleaning the basement out, I'll have the task on my Remember the Milk iPhone app, but I'll also have a note which details the sub-tasks that are involved. I will usually append a C to the line of each sub-task I complete.

It's not perfect, but it's much simpler and more convenient than some of the schemes I've found floating around here.