NVIDIA has quietly disabled overclocking their mobile GPUs in their latest driver update (version 347.29), claiming that mobile GPUs were never meant to be overclocked and it was enabled by accident. This issue was found when it was found that after updating to the latest driver, their clocks dropped back to stock and they found that their GTX900Ms overclocking function was disabled. Here is a reply by one of their representatives on NVIDIA Geforce Forums:
Unfortunately GeForce notebooks were not designed to support overclocking. Overclocking is by no means a trivial feature, and depends on thoughtful design of thermal, electrical, and other considerations. By overclocking a [...]