System Information
Win 7 Ult 64
GeForce GTX 580 1.5GB

Blender Version
Broken: -
Worked: never

Short description of error
I know this falls under "works-as-intended", I'm still throwing it out as a reminder of a feature that is half functional.

Can not navigate when Circle Select is invoked.
Why not use the same paradigm as with Knife Tool, and PASS_THROUGH navigation. Have a drop down to choose "Panning" that will allow (even custom navigation) to PASS_THROUGH the Circle Select. Basically same principle as with the Knife Tool.

As is, it's really hard to use Circle Select effectively, as you have to constantly exit and re-enter the tool in order to complete desired selection. Because you have to navigate the model to achieve it.

One thing at the time, that would be most important!
Another useful thing would be to set the Circle Size like the sculpt Brushes - with one hotkey+mouse gesture. Like the Sculpt Brush Size, F + LMB (drag L / R). I would imagine that wouldn't be too big of a deal, as the code is already there.

I apologize again, because this is one of those situations that could go either way bug<>works-as-intended. I do believe that it would enhance the productivity of the Circle Select so much that I felt I would draw your attention to it.

Thanks.

Exact steps for others to reproduce the error