Google has patented a new radial menu system. Many usability texts I have read advocate radial menus because of the proximity benefits, Kirill Grouchnikov even blogged about how nice they are over the more common context menus. They do have some usability issues however:
1. The target area gets smaller the larger the number of menu items.
2. It is difficult to travel through all of the options via a keyboard and screen reader depending on how you allow the arrow keys to work, especially you have multi level radial menus.
3. Any uncommon navigation method can be distracting to new users.
Google of course does not need to implement the patent but I for one am interested in seeing what might arise. Google's patent for a pop-up radial menu that uses two fingers to operate one is an anchor and the second is selector.
The main issue with pop-up menus on touch screen devices is that they are always activated via holding down a finger on the screen. It would be great if they could be activated instantly then such a menu could replace the on screen buttons. However, the clear instant access that on screen buttons provide makes me think that radial buttons will only be of minor benefit. I hope Google can prove me wrong, then perhaps we can all start using radial menus when they seem like a good idea without fear of instant customer revolt at a new paradigm.