For the purpose of answering questions along the lines of "Is X Christian?" (several examples of which have already come up--and undoubtedly will continue to come up, especially once the site is public), I wonder if we need a definition of "Christian."
As I mentioned in one of my own answers, the word can have different meanings in different contexts. If we choose to develop a definition for this term, it probably needs to be multi-faceted, to account for varying contexts.
Although it might be a bit of a hairy task to come up with (a) definition(s) we can use for this site, I suspect it will make the site much more usable. And in my mind, it is okay if we answer the question "Is X Christian?" with "Yes, and no--it matches definition A, but not definition B." At least we're able, this way, to provide a useful answer to the OP.
In response to Mark's answer, I think the nature of this site is sufficiently different from the nature of SciFi, that it is reasonable to consider other answers to the dilemma. Many people are likely to come to a site like this with difficult questions they are struggling to answer or resolve in their personal faith. And asking "Is X consistent with Y faith?" is an important part of exploring and coming to understand that faith.
The same can't very well be said of Science Fiction. Those of us who enjoy SciFi can easily do so without a clear understanding of whether what we're enjoying is SciFi, Fantasy, or some other genre.
This also brings up the point that SciFi does not have a clear definition (or definitions), in that a single work of fiction of work can cleanly fit into multiple categories simultaneously.
Perhaps a similar argument can be made of religions doctrines and philosophies, but to me the concepts seem significantly different. I don't think anyone would say the belief that "Jesus is the Son of God, but not divine" is "partly Christian, partly Muslim, partly XYZ."
Perhaps what I'm getting at, is that I think we need some context in which to discuss various philosophies and doctrines that may appear to have some element of Christian influence, but which upon further investigation likely have very little to do with Christianity, as I think any of us would define it.
For example, many Buddhist and New Age friends claim that their ideologies are completely compatible with Christianity. I don't know of any Christian ideology that would agree with this, though. So if someone approaches us with the question "Is Buddhism compatible with Christianity?" or "Is Yoga compatible with Christianity?" we need a context in which to answer it. And saying it's off-topic does not seem like the proper approach.
I'm not advocating for a dogmatic definition of Christianity that is designed to exclude anyone from participating in this site. I'm simply looking for a context in which we can answer these sorts of questions, which I'm sure will come up.
Perhaps the answer is to steer away from defining Christianity, and instead finding some other context in which these questions can be asked and answered.