I think the best compliment I can pay Aza Raskin is that whenever I look at one of his designs, I know immediately that it's his. He's got a focus for circular designs combined with an emphasis on minimal displays that convey a lot that's a signature look in my mind.
This stuff he's doing for Mozilla thrills me. It's great to see him working with a huge company.
I'm a bit skeptical. The circle is loved by designers, but it does not seem to survive in software that is actually being used by people. There are few pieces of software that uses circular control elements - the few that I can think of (the logitech mouse, LabView) don't handle well.
In this case, the design doesn't function as a circle. It changes to a linear list once you move your mouse. The circle is just there as a placeholder.
Have you used Raskin's music site Songza? It's a great example of circular navigation that works really well.
It does not work for me personally. I don't like the way that the options appear in places that I did not predict they would appear in. When I interact with anything, I want it to behave exactly the way I expect it to behave, and to do so consistently.
The songza site does not behave as I expect it to, and even after I learn how it works, it does not behave consistently in its own mould. I click an item and up pops some 4 arrow thing. When I move over some arrows, yet more things pop up and on some other arrows, more things don't pop up, and there is no hint as to which will cause things to pop up or not. So even though one might learn how such a navigation works on that particular site, as soon as you go to another site, you will have to relearn again which of those arrows will cause popups and which will not. Contrast that to a right click menu which always indicates which options will pop out.
I don't think circles are good navigation tools, for the reason that there are very few popular tools which use circles as their main navigation mode.
It seems like you are not arguing against circular navigation in general, but specifically the navigation on songza.
Your problem with the unpredictability of the menus in the songza-style navigation could very easily be fixed by simply adding an arrow to each item that contains a submenu, just like the typical context menu.
An arrow could be added on the tip of each leaf of the songza navigation circle that uses has a submenu. The arrow would visually indicate that a menu will pop out if the mouse hovers over leaves with these arrows. This would function exactly as the arrows on the typical context menu.
I used to love this extension, until it became incompatible with a new FF, whereupon I promptly ditched the mouse.
A point in support of neither: the circle is an excellent design element in gesture-related selections because all edges are equidistant from the center. Duh. The not-duh part is this: usually 8 arcs is the best division of space, but 8 is a bad number. It's not too big nor too small, and using the circle leaves you little wiggle room, such that you start constraining your design decisions to it.
When it works, it works great. When it is slightly off, it is quirky, because it is tempting to just throw in some extra options to fill up the 8 parts of the circle.
This stuff he's doing for Mozilla thrills me. It's great to see him working with a huge company.