Considering purchasing a 3D mouse, but I'm unsure (even after extensive Googling) as to whether or not Blender is fully compatible. Sculpt mode is apparently a yes, as is Object mode (please correct me if I'm wrong!), but what about Edit mode?
Yes, Blender is fully compatible. I use a 3Dconnexion SpaceNavigator with Blender both in Windows and OS X daily. It works great in all 3D views/modes but also in (for example) the Node Editor where you can pan around and zoom in/out.
Note: I haven't used the buttons much since there are only two on this particular model, but for navigating around it is really a time saver.