The verdict is still out on CBN. At first (as far as I know) people assumed strong cannabis was just weed with lots of THC, but they're now finding that CBN and THC act together to create unique psychoactive affects. Indicas generally have more THC to CBN, causing the stony couchlock high associated with the likes of White Widow and Afghani. However, sativas, like haze, have a higher CBN to THC count, which may be why people say sativas are "trippier" with some visual affects occuring (I've only experienced "heat-wave" visuals once from weed though).