We demonstrate an optomechanical system employing a movable, micron-scale waveguide optically-coupled to a high-Q optical microresonator. We show that milliwatt-level optical powers create micron-scale displacements of the input waveguide. The displacement is caused by a cavity-enhanced optical dipole force (CEODF) on the waveguide, arising from the stored optical field of the resonator. The CEODF is used to demonstrate tunable cavity-waveguide coupling at sub-mW input powers, a form of all-optical tunable filter. The scaling properties of the CEODF are shown to be independent of the intrinsic Q of the optical resonator and to scale inversely with the cavity mode volume.