Blender Version: 2.75a Build: c27589e (Oficial)
Same behavior in version 2.75.4 Build: 4ac5859 (Latest Build from Buildbot)
System: Lubuntu 14.04 (3), 64 bit (LTS), GTX 285, NVIDIA Proprietary Drivers, Opteron 285, 16Gb RAM
Description:
Geometry displacement isn't updating 3D View Editor as we move the numeric slider (numeric button) present in the Influence Panel of the Texture context in all Modes (Object, Edit, Sculpt, etc) but Rendered mode. Tests were made with all textures.