It was 2 years ago when I started using Songza – musik search engine. The site was designed by very well known usability guru and ace software developer AzaRaskin (Mozilla). And what I liked first and most was pie menus.
There’s very simple but useful principle in ergonomics known as Fitt’s Law:
Time required to rapidly move to a target area is a function of the distance to and the size of the target.
The bigger distance and smaller size of the target – the bigger time needed, and vice versa, bigger objects placed closer require less time to navigate to.
This is exactly what makes pie menus so efficient because all objects are on the same relatively small distance from the center and targets are relatively big. There’s also another point to pie menus, since distance is the same, the experienced user has only to remember the direction which is pretty easy and minimizes time required for turning user goal into actual movement. Think how easy it would make applications like finance software and app development software to operate.
From the implementation standpoint it is evidently more difficult to develop such a menu, but the problem is rather in the tradition itself. You almost never develop conventional (plain) context menus on your own these days – all you need to do is just specify your item list in a configuration file or so and attach action listeners to them. Although there started appearing solutions for pie menus too. RadialM, for example.
Speaking of notable examples of pie menus: