Given the site being relatively new there are many (and will be eve more) questions like :
Are questions on topic X is - on-topic or off-topic?
Here are some glimps:
Computer Vision questions are on-topic or off-topic?
Are OpenCV questions on topic?
Are questions on numerical analysis on-topic?
Is this the place for Neuroscience related questions?
Do hardware benchmarks questions have lasting value?
Where do PID loop + other control systems questions go?
I think it is best that we organize a sort of rather longer a prior list of what we think is on-topic or off-topic right away. Over time we can edit this as well, but we can find one central place that keeps definition refining all throughout.