Obviously questions not about Blender would be off-topic but what should be the general yardstick for off-topicness?
Update:
Since the site has moderators now and we can better address on/off-topicness, we feel it is time to start rolling out some of these to our help page where needed. This is so we can have one definite place to point new users to.. etc.
It is also worth noting that none of these were thought up by any one person. These were decided to be the norm and are only here because of them being agreed upon by the majority. Poke around meta or browse through the discussion tag to find these.