It isn't fully open-ended, however, requiring that you download an SPD file from the OCZ forums, which the SPD tool can then flash the memory with. The reasonings are sound. Particularly with the high-end modules and chipsets that supported non-JEDEC certified speeds, people want and need greater flexibility over how to configure their memory. Further, many memory modules will require different timings based on what chipset and what CPU is being used at the time. For people that are really in to overclocking or tweaking, this is definitely an interesting tool to look at.
The SPD-Z utility only works with OCZ memory modules, and is a Windows-only program. The program is considered to be in beta, so beware if you are planning on tinkering. They mention it should work with any motherboard, regardless of the existing chipset.