Checking for updates to any controls on Windows Forms?

I have a routine in my Form_Closing() Event that checks each control on my form that could change in value. If the value changes then a boolean variable is set in the controls Leave() Event. This isn't working real. Is there a better way to check if any values were changed. For example, if I load some data into some TextBox controls and the user changes some of it, what is the best and easiest way to flag that?

Thanks!