Canon Musings Found Online

Though not 100% work-safe even in the link, this guy touches on the canon of Buffy: The Vampire Slayer, the Star Wars Expanded Universe, and he really goes to town on the canon policy of the BBC in regards to Doctor Who, a canon policy which is to not have a policy.

There are also some great quotes in there. Paul Magrs, for instance:
"Its a curious irony, I think, in a series with a rabble rouser as a hero, and in a narrative about multiverses, alternities and possibilities, that the fans of this very show want to close possibilities down. Sometimes its as if fans want reality dictated to them- definitively. Canonically. They want parameters setting and concretising around them. Maybe they want a stable universe after all..."
Seeking order in a disordered and chaotic universe? Perish the thought! It's not like we ever assign wrong-headed narratives to history in order to give the chaos of history a narrative, after all . . . oh wait.

Here's an interesting idea from Paul Cornell:
"I can’t think of any other fandom that assumes they have a canon when nobody has ever told them that they do. Especially since our show itself declares that it doesn’t now have, and probably never did have, a canon."
So far as I know, the answer to his question is the Holmes canon. While Doyle was involved with listings of his favorite or fan favorite Holmes stories, I'm not aware of him ever specifically discussing the 'reality' of Holmes and whether certain fan-discounted, hard-to-find tales were or were not part of the Holmes continuity. Certainly, given that he continued to write mystery stories even after the death of Holmes, I'm sure the idea of a reboot might've amused him.

In any case, though, the amusingly-named "Teatime Brutality" blog from which those quotes came has some other interesting observations and thoughts on the question of canonicity, some of which I've never had to ponder not being a Who person and other general bits I might've considered but never had need or chance to put to paper. But if you're interested in the topic, it might be a nice read.