I have!
I sat the BJCP exam on the day after I helped out at the NSW state comp.
Not sure how I did, in the exam, with the theory and styles etc (memory stuff), but I think I gave a fair reckoning of my judging skills, both in the exam and at the comp.
BTW, if anyone got judging sheets back from me and wants more info, based on what I wrote, sling me a PM and let me know what you want feedback on (a quote from my comments might help jog a memory. Hopefully, I won't get inundated.
In my opinion, the BJCP course is great, and the tastings/style familiarisations really helped me with recognising flavours (both right and wrong). I discovered that I am one those who can taste diacetyl, but have little sensistivity to acetaldehyde. I am very sensitive to phenolics and acetic aromas (prob from brewing good and bad wheat beer). My nose and tongue are both good at picking up hop astringency and oxidation, which were both a little too well represented in the State comp, in one of the styles I judged. I tried to provide helpful, corrective feedback, but it was a busy day, and I may have missed writing some relevant comments.
The competition judging is at least as useful as the BJCP learning, and both go well together. After tasting those comp entries, I get a feel for where I am as a brewer, and as a judge.
Looking forward to more judging, but maybe not another BJCP exam. If I did, more study would be required, for sure.
Seth out