I find Circle extremely useful and it seems to be just what Windows has always missed. However, there's one thing about Circle Dock that still needs to be refined. It's the way Circle Dock gets toggled.
Yes, bringing the mouse to the edge of the desktop is fine, however, it's too much effort. The same can be said about keyboard shortcuts.
The mouse middle button comes real close to the entire idea of Circle Dock. Using it you can have Circle Dock show wherever your mouse cursor is at the moment. However... The middle button is heavily loaded with functionality in other Windows applications. For example, in my Opera browser, I use it to slide the page and to open a link on a new tab. So the middle mouse button is not a solution either.
What I want to suggest is that the left mouse button can be used in an unusual way. What if Circle Dock is toggled when the left mouse button is pressed and then held for some time (a second or two)? This would allow to have a very comfortable way of showing Circle Dock right at your mouse cursor.
Alternatively, mouse gestures can be used. But in my opinion, the left mouse button being held for a second would be the best and safest approach to showing Circle Dock regardless of the application you are currently working in.