Hey there! I'm busy updating my books for Excel 2013. So not a lot of time to post.
Here's a quick tip you can use to add comments directly into your formulas.
Got a complex formula that you know you'll forget in 6 months? Add some comments to them by using the N() function.
The N() function allows you add documentation directly inside your cells. To use it, simply add a + sign to the end of your formula, and then pass some text in quotes to the N function. For example:
=Sum(A1) + N("Yes … I am summing one cell.")
Here is a quasi-real example:
Once you use the N function, you can simply look in the formula bar to figure out what the hell you were thinking when you wrote that formula 2 years ago.