Bevel Tool and Mac mouse when using the Bevel tool you can change the number of segments by scrolling the middle mouse wheel. At least when you are working under Windows. But how to simulate that with the Mac mouse (I know how to Rotate, Pan, Zoom with the Mac Mouse).
After you've left-clicked to accept the radius, the bevel-tool is still active and you can 


press numpad + / - to change the segment count. If you don't have a proper numpad: in Preferences, go to Input and check Emulate Numpad
or.. press F6 and adjust segments from there: