There seems to be some confusion as to whether a question can be asked if the questioner knows the answer. I have asked some questions where I knew the answer and have often received answers I was not aware of. In addition as I have mentioned in the past new questions are needed to keep the site fresh and interesting. What are the thoughts of others on meta?
I would add, though, that people who do this should be very careful to avoid a pitfall that's naturally associated with it: skimping on question quality. People who ask questions they don't know an answer to are naturally motivated to put as much detail and motivation as possible into the question, to help others give answers that are as helpful as possible. People who already know an answer, by contrast, are much more likely to post just enough of a question to serve as a set-up, in their own heads, to the answer they know.
Consequently, I think it's important to make sure to write all questions from the point of view of someone who doesn't know an answer, and accordingly, include as much information as possible to help answerers. In particular, if your Q&A is motivated by the fact that you were curious about something, found an answer, and want to share it with the world, you should remember what you were thinking in the curious phase when writing the question.
UPDATE: Reflecting on this question it seems to me that it's worth drawing a distinction based on where the question is coming from. Is it plausible to say that the question is based on curiosity about something, where knowing or seeing one thing makes you wonder about something else? In that case, you've probably got a question that will fit our format well. On the other hand, if the question mainly comes from knowing the answer and wanting to let people know about it, it may be difficult to express it in a useful, non-leading way.