After the mergers with psychology and the others, we've cast a fairly board net consisting of all things mental.
However, that's everything when you think about it ;-), so I'd suggest voting to close questions that aren't specifically about understanding or applying some psychological phenomenon.
The two obvious edge cases here are design and self-help, which must be taken on a case-by-case basis, but a good general rule would be that if the question doesn't primarily care about the working of the mind then its off-topic.
ON-TOPIC: How do affordances affet the usability of devices?
OFF-TOPIC: Does this design make good use of affordances?
ON-TOPIC: What does Maslow's Hierarchy have to say about how to improve our level happiness?
OFF-TOPIC: What are some psychological sound suggestions for becoming more successful?