What is the Holocron? blog:
Are the entries in the Holocron sorted as canonical & non-canonical? Are there various degrees of "officialness"?
The database does indeed have a canon field for each individual entry and for sources, though the canon level of the entry would overide the canon level of the source since it factors in other sources associated with that entry. When determining canon levels for individual entries, anything in the films and from George Lucas (including unpublished internal notes that we might receive from him or from the film production department) is considered "G" canon. Next we have what we call continuity "C" canon which is pretty much everything else from the EU. There is a secondary "S" continuity classification used for older published materials created when there was less attention to making everything in the EU fit with everything else in the EU. But, if it is referenced in something else it becomes "C". Similarly, any "C" canon entry that makes it into the films can become "G" canon. Lastly there is non-continuity "N" which we rarely use except in the case of a blatant contradiction. Any contradictions that arise are dealt with on a case-by-case basis.

"The Go-To Guy" article on www.wizards.com
Wizards: Let's say that you come across two or more contradictory sources while chasing down a reference. How do you decide which one to accept as "canon"?
Leland: Everything is looked at on a case-by-case basis. Among the factors we consider: In how many sources does this particular fact appear? Which source has the largest audience? Which explanation is the coolest? Have we been told by George Lucas to avoid this topic? If, after weighing all those variables, the answer isn't yet clear, the issue is presented to an internal group that makes the final determination as to which source is "correct."

Holocron continuity database questions thread
Are deleted scenes considered G-level?
Yes, unless they conflict with something else seen in the films or if the reasoning behind deleting the scene keeps it from being continuity.
[ADDENDUM: this applies only to deleted scenes publicly released]

Might we discover what the non-obvious G-level elements are, some time after Episode III?
I don't forsee that happening. Sorry. I really wouldn't take too much stock into the difference between G-level and C-level because the lines between the two are so blurred.
[ADDENDUM: to clarify, I mean blurred to the public. Since we started the Holocron, internally, we are well aware what information is G-level]

Of the two official continuities (the films alone continuity and the films + EU continuity), is one more 'official' than the other; which is the 'true' Star Wars universe?
You're asking the Keeper of the Holocron, so of course I'm gonna be a bit biased. The "film purists" aren't the types to be hanging out on the boards so it's unlikely you'll hear much official rebuttal around these parts. With that said, the reality is that a huge number of people who have seen all 6 Star Wars films have never played a Star Wars game, visited a Star Wars website, watched a Star Wars television program, read a Star Wars publication, or purchased a Star Wars action figure or collectible. It would be great disservice to discount these people as fans.

regarding the 3d clone wars cartoon and the live action star wars tv series, are they g-canon or c-canon?
So far I'm using the term T-canon for the upcoming animated series and live-action series. Nothing prior is being considered T-canon.
[ADDENDUM: This also applies to the theatrical release of The Clone Wars. T-canon falls between G and C.]

I'll add more to this list when I can.