I find it a bit hard to parse the pie menu. My eye has no obvious place to start or end in reading the options, so i try to pick one quickly. Vertical menus have an explicit order (if not alphabetical, an intentional one) which helps I can scan quickly. Also, when I go into a sub-menu, I don't lose the context of the parent (which is also avoidable in pie, but not in the x10 demo shown).

We've been trained from an early age to process lists. Lists are cool.