crussader
Flush
For me, a Grail set, would be the set that made me so satisfied, I quit the hobby. Pure and simple. As long as I'm here, digging through pictures and classifieds for other sets and chips...I haven't found my Grail..
Conceptually, I would say that's close to a good definition. However, I don't think it would necessitate quitting the hobby.
I have found my "grail" set but it hasn't lessened my interest in the hobby. I still enjoy looking at new chip discoveries and helping those new to the hobby. The only difference is I no longer have that constant, driving obsession to find the perfect set. I have peace and now enjoy the hobby rather than obsessing over it.