I used to use TheBrain for monitoring and keeping up to date with state, federal and local tax and reporting requirements. So not exactly, but yes I did (and still do) use it for structured and referential access to documentation. I speak in the past tense not because I stopped using TheBrain, but because my position changed so I no longer need to track this any more.
TheBrain is the only software I've found that allows me to reference URLs, notes, and files in the same "container". I found (and still find) it invaluable for archiving the form and instructions, making notes of common pitfalls or questions about them and including links to not only the source site, but related information in a structure that's easily searchable and displayed my information in a non-overwhelming coherent manner. I agree, TheBrain 9 will improve on this capability yet again. I'm already starting to see how including previews or the web site in the preview gives me more immersion in my data and removes some cognitive roadblocks. I think this original use was one the things that really cemented TheBrain as the center of my "electronic" life. I saw how effective it was at allowing me to keep on top of things in a manner that made sense to me. As I experimented and fine tuned the structure so it was more efficient and effective at communicating the information I needed, I saw ways to carry it over to other areas. I'm currently using TheBrain for documenting database and reporting references, scripts and other references, in addition to documenting and keeping information related to my personal interests, and as a work and personal log.