In previous versions of Blender I've used, pressing or releasing Shift while holding MMB would switch between orbiting and panning, without needing to let go of MMB. In my fresh installation of Blender 2.77 (on Ubuntu Linux 16.04), pressing or releasing Shift while holding MMB does nothing; if I wasn't holding Shift when I pressed down MMB, then it would stay in orbit mode, no matter what. How would I restore the old behavior?
Got to File > User Preferences > Input > 3D View > View 3D Rotate Modal and add a new key combination
Set it to
Switch to Move and add any key combination you like.
I did not succeed settings it to work with the Shift key though, it seems to not like "modifier keys" on their own, but most other combinations will probably work.