The CUDA 5.5 Release Candidate isn't available publicly yet, but for registered developers with their Developer Zone the new release provides:
- Multi-process MPI debugging & profiling
- Single GPU debugging for Linux
- Step-by-step guided performance analysis
- Static CUDA runtime library
- RPM/DEB packaging & new NVIDIA repo
More details on NVIDIA's CUDA GPGPU tool-kit can be found at developer.nvidia.com. Expect the official NVIDIA CUDA 5.5 release later in the summer.