So, in terms of Star Wars, much of what is and is not canon is potentially in doubt.
See Disney takes a chainsaw to the Star Wars expanded universe for further info on this.
Now, from what I've read elsewhere, the expectation is that all post-RotJ events will be nuked from orbit: they will no longer be canon. The reasoning behind that expectation is to allow the Episode 7 script to be freely written without any concerns about whether or not it will clash with EU material.
Update : Per this post on Starwars.Com, the new canon levels have now been fully confirmed:
While Lucasfilm always strived to keep the stories created for the EU consistent with our film and television content as well as internally consistent, Lucas always made it clear that he was not beholden to the EU. He set the films he created as the canon. This includes the six Star Wars episodes, and the many hours of content he developed and produced in Star Wars: The Clone Wars. These stories are the immovable objects of Star Wars history, the characters and events to which all other tales must align.
While the universe that readers knew is changing, it is not being discarded. Creators of new Star Wars entertainment have full access to the rich content of the Expanded Universe. For example, elements of the EU are included in Star Wars Rebels. The Inquisitor, the Imperial Security Bureau, and Sienar Fleet Systems are story elements in the new animated series, and all these ideas find their origins in roleplaying game material published in the 1980s.
In the light of this development, should we be looking to revisit the Star Wars questions on this site? We have many questions which have answers based on material which was in canon at the time they were asked, but which may no longer be in canon in the future. In other words - we have many questions with potentially wrong answers.
Is now the time to start discussing this issue? Is now the time to start thinking about how we handle any future Star Wars questions? Do we need to go back over past questions?