Before getting too excited, the hardware drivers haven't yet implemented the support. It was back in December that core Mesa received its treatment for compute shader support and came with Intel's i965 driver implementing CS.
Since then, Nouveau developer Samuel Pitoiset has been readying patches for compute shader infrastructure in the Gallium3D world. The Mesa state tracker changes were reviewed while he's been working on NVIDIA Fermi CS support. Samuel has managed Nouveau Fermi patches for compute support but doesn't yet have the Kepler support in good shape.
Landing today in the common Gallium3D code and Mesa state tracker has been a ton of the compute shader work that's shared between drivers. Hopefully Samuel's Nouveau NVC0 compute shader patches aren't too far behind while the RadeonSI support won't be far behind.
Mesa 11.2 though is being branched next week so unless there's a mad rush at the end, the ARB_compute_shader support won't appear for the Gallium3D hardware drivers in a released version of Mesa for another three months.
No other news to report right now on the likelihood of Intel getting GL 4.0~4.1 support in the next week (still blocked by FP64) or whether Nouveau NVC0 will get OpenGL 4.2 (still blocked by shader_image_load_store) and RadeonSI is blocked both by the shader_image_load_store and the ARB_shader_atomic_counters extension from GL 4.2 compliance. The compute shader support is one of the big ticket items of OpenGL 4.3.