Just an observation on round controls, from the point of view of user interface design.
Since round knob controls are not a standard control type, they tend to be implemented differently every time. Sould I click and drag up and down? Drag left and right? Try to drag in a circle? Simply click on the point where I want the control to be set? All of the above? (The circle motion, while it may be natural for a physical object, isn't so natural with a mouse.)
What happens if you choose the wrong method of operation? (When I first tried one, I didn't get it right until the third try.)
What happens if you drag too far? For example, with the Probe skin, I have twice so far accidentally taken the volume control from mute to full on, blasting my speakers, ears, and neighbours in the process. I can't seem to replicate this behaviour on command, but it's very annoying when it does happen.
One method to protect against this might be to allow only about 300 degreess of rotation instead of 360 degrees.
Be careful not to put form over function. I'd suggest we don't see round controls often for a reason.