I was looking at Koltar's thread about Star Wars and have been thinking on it quite a bit, how many of us play in game settings that have significant "canon" of material to draw from?
When you do use such a setting (even if its drawn from TV, movies, non-game sources), how much canon do you use?
How much do you ignore?
I keep thinking of several canon heavy settings I enjoy, and also how I'd probably re-start some and run completely differently with just the basic idea and nods to the material (Transformers, for example, is one of mine.)
I also run a few times a year game where the PC's are in the Marvel Universe (but a radically divergent one thanks in part to the existence of these particular heroes.)
For me, I take a good hard look at any canon based material and decide if I can't do my own things with similar plots. I can't always get what I want out of others settings, on the other hand there is a huge appeal to playing "Star Wars", "Star Trek", or whatever, common themes that fit those settings and don't detract from them can be fun, but often the baggage of expectations are a lot to live with--especially if someone isn't the best GM without the baggage.
I'm pretty proud of my record for most games, I think even with canon settings I do decently, but there are reasons I often choose to go with "like X" rather than with "X", because it allows me more freedom to make the heroes, the player's characters, without interfering NPC's, or without expectations of meeting/greeting and dealing with others constructs I don't want. While I can reject, say all the Star Wars movies after Return of the Jedi (the prequels) these days I'd have to explain to my players why I did that. (For me, I see them as Rebel propaganda to discredit Darth Vader's actual accomplishments as a Starfighter pilot and a jedi later.)
I like canon as a reference and idea generator. It also locks out a lot of good ideas. I only follow canon when the players insist.
(and then I let them run the game instead ;) )
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I play a lot of historical games. That's a lot of canon. When I play them, the world is as history says it was, but from that point on, things can, and sometimes do, go very differently. In my current Aces and Angels playtest, the PCs drove off the second Japanese invasion of Wake Island in Dec. 21st, 1941. The game is thus already into alt.history in the second session - the first being Pearl, of course.
-clash
I like the challenge of working around it as a GM, especially when the property is very well-known or it's actual history. However, when I want leeway to change things I say so up front.
When I run games like Star Wars of Forgotten Realms I use all the canon that 1) I know and 2) sounds fun. If it fails either check it's gone.
Again, if you count historical games, I actually use a LOT of "canon". Not to mention that besides that, my Legion of Superheros game has a lot of canon associated with it; but then, I'm a Legion fanboy the way other people are SW or Star Trek or FR fanboys, so I know all the canon pretty well by heart.
Even then, though, I make it very clear in my games that the GM is the arbitrer of what canon is or is not used, and the players should NEVER assume that something they read or saw outside of the game is "true" inside of the game, unless I explicitly confirm that it is. I think you have to do that right off the bat: the canon must be there to serve the GM, and not vice versa.
RPGPundit
I don't play much with a lot of Canon, but in cases where I have it's not a problem.
As long as everyone understands from the point in the history in the setting that players come into game none of the future stuff has happened yet. Also, I try to keep in mind which actions affect the cannon and how they affect it.
If the PCs do something that would change the actions of "canon" characters then they change, if not, they don't.
Pretty simple, unless you get some tard that gets all hung up on what happened in the movies or books.