Like Gina Trapani, I found myself returning to a simple "todo.txt" after each excursion into a heavier-weight, more complicated task or project tracker (and my original todo.txt is probably older than she is :).
My todo.txt format has gotten a little more complicated over the years, but only a little. It now includes a date/time stamp at the top of each "chunk," which is a shortish list of tasks for one day or so. I could have added a timestamp at the beginning or end of every line, but that results in more, cluttered output.
These programs help by:
1) merging multiple todo.txt files into one file, in the case that I've copied my todo.txt to another computer, worked there, then returned to the original and worked there too, and
2) sweeping completed tasks into a "done.txt" and forwarding older unfinished tasks to today.
todo-merge [--no-color] <file1> <file2> todo-sweep <todo-file> [<done-file>]