I would also like to promote this idea. Evernote could be the first at implementing something completely new.
My example is for my shopping list I currently perform on paper. The list is comprised of items I normally want to keep in stock. Each item has a clear circle which I fill in with pencil reflecting its status.
Clear = enough on hand.
1/3 filled = buy more if on sale
2/3 filled = buy if available or at that store
Filled = completely out (buy ASAP)
The advantages:
I never have to recreate the list, and can always add another item, or even "one time" purchases.
I also have items grouped based upon the type of store. (ie: groceries, automotive, electronics, etc.)
I just erase the pencil when I have correct stock on hand. Or reduce the filled in portion if not enough were available.
I can purchase effectively by prioritizing the filled circles first.
I also like the OP's idea of multi levels for simple project steps status levels.
Please consider a way to add "multi-level checkboxes".