PieMenus rely, once you have grown accustomed to them, on your MuscleMemory. You perform an action often enough that you can do it without thinking.
How about and example of this starting to go too far? The OperaBrowser can use GestureRecognition for closing a window:
Except when it doesn't work.
So, I imagine that changing the entries on PieMenus will cause huge confusion. Changing the sort order of the entries or inserting/removing entries would be the worst, since every item in the menu will have a new position.
Changing the meaning of one position will only affect that command or sub-menu.
Efficiency
I'm reminded of the RedBlackTree algorithm. It's a binary tree (PieMenus seem to have four to eight entries per node?), but the main point is the one attempts to keep all legs of the tree to similar sizes.
Actually, more important would be to keep related operations together, and most frequently used operations near the top of the tree. This departs from the RedBlackTree since most leaf nodes will be N levels down.
The problem is, your RedBlackTree can be shuffled if necessary, and it will still work just as efficiently. MuscleMemory requires a training period to reach maximum efficiency.
I wonder how long it takes to TrainMuscleMemory?, and what software can do to accelerate this without forcing the user to practise? -- DigressingOne
DebianGnuLinux has some tools for generating menu structures, and I believe these have an assortment of heuristics which can be used for balancing up the tree sizes. http://packages.debian.org/menu -- MatthewAstley
Solutions
(ha)
Well, it sounds like PieMenus need to be ConfigurableUserInterfaces, with all the complications this entails and the usability problems that PerpetualBeginners? have with reconfiguring their software.