The caret position property is already there in the Presentation Framework. I'd prefer to also have it in Winforms, as it currently doesn't exist.
I could technically try to keep track of the caret position by keeping track of the number of characters inserted or deleted, and the pressing of the arrow keys, etc. but there are a variety of cases in which the caret position will change, such as when the user clicks with the mouse to a different position in the text. Suddenly, the task of keeping track of the caret becomes difficult.
It may be a useful property for TextBox in general, but I need it to change the color of recently typed text, which is difficult to do when I don't know what the recently typed text is.