I've met two Forgotten Realms "canon lawyers" so far. I had no idea what these guys were complaining about in the 3.5E
FR game I was playing in. At the time, I was relatively clueless about Forgotten Realms for the most part. I had never read any of the
FR novels and I didn't have any
FR splatbooks or modules at the time. (Even today, I still have not read any
FR novels).
After awhile, these
FR "canon lawyers" got really annoying. Though it didn't turn me off from the setting.
For other settings such as Eberron, Golarion, etc ..., I haven't met any hardcore "canon lawyers" yet for these particular settings.