I do the same thing, but not just when working alone -- I just use a a text file in dropbox + vim.

For more complicated tasks I create check lists before hand (to make sure I cover the edge cases), and sometimes create "Testing:" check lists to make sure I also test all the edge cases. I also have free form text when I'm thinking about a problem, or when I get feedback about different things.

It's organized by day and is invaluable, with a simple search I can find out what I worked on any day -- really good for reflection and marking progress.