The new application uses SIMD Maths and can delegate the calculations to a CUDA-capable GPU. My personal tests with a Nvidia GTX 260 (GT200b) revealed a speed increase of up to 24 times compared to the (also very fast) PTGui 8.3.6 stitcher!
The stitcher is still in an early beta state, so don't expect it to be feature-rich. However - integration in PTGui is already working.
PTStitcherNG is available for Windows, MacOS and Linux (x86). The most current version can be downloaded here.