The official position is that ANY novel other than the novelizations of the movies is part of the EU. If something from the novels gets put into a movie, such as Coruscant (Only the name is Zahn's, and it is Zahn's) or the YT-2400 (from Shadows of the Empire) then that becomes canon, but the work it is derived from is still Expanded Universe. Likewise, if an item from an Infinities work is incorperated in the Expanded Universe, then the item itself is EU, but the original work is still Infinities.
At this time, the canon consists first and foremost of the movies. After that, the novelisations and Radio Dramas are canon, but if they are contradicted by the movies, the movies take precendence. Etcetera on down. The Incredible Cross Sections books may be lowest-level canon, as they are derived directly from the movies and comments have been made to that effect. But the EU is a perfectly valid source for information, at least moreso than fanfiction, so I don't see why you bring it up.
If anyone disputes this, I can go get my quotes list.
Oh, and the Star Wars.com site has no official standing as a resource that I am aware of.