I’ve hunted around a bit but can’t find a definitive answer to how values are translated in bump mapping. It seems that with the positive setting for Nor that white is higher than black, but is this because white is raised or because black is lowered, or some combination. I tried to compare a bump mapped plane with an plain one but still couldn’t tell which way it was going.
if iremember well white is up and black is down or as a hole
check out the wiki page for bump mapping!
and grey is between the 2
SAluations
Yes, ricky is right, as far as I know, neutral gray (0.5/0.5/0.5) marks no elevation, while more white causes an elevation along the normal pointing outward, and more black along the normal pointing inward (or the other way round, using the “Neg” button). The strength of that effect is controlled with the “Nor” slider but I’m not sure how the settings are to be interpreted with Blender units (absolute scale). It also depends on the bump map you’re using so that’s probably not very easy to answer. However, on the other hand it’s not what Bump mapping is supposed to do: it’s all about faking and not about accuracy.
By the way, keep in mind that bump mapping has NO effect on the actual geometry of a mesh. That means, a flat plane will always stay flat if viewed from the side, even if a bump map is applied.
That’s why I want parallax maps instead 
When will it be coded into blender?
Care to explain what the difference is? Is it really necessary besides Bump / Normal Mapping and Displacement? Do other rendering engines support it? I heard about Parallax Mapping already and read a bit about it, but I still don’t get why it would be better in such a situation.
I agree that Blender doesn’t handle bump maps in a great way but it works. It will be coded if someone does it, why not yourself? Other than that, the question is rather…unnecessary. As you surely know 
Normal maps do work better than bumping, in my experience. Quite frankly bump maps barely work compared to other 3D packages which really shine in this department.
Read a little more about parallax maps, then. They actually simulate displacement in a way other than simply changing the diffuse, and without the use of extra vertices. They look genuinely bumpy and even cast self-shadows (deep parallax maps) and they warp textures and self-obstruct and all that. plus, it works in realtime. Anyway, you can tell which way is up that way.
I already know how parralax mapping works, and parralax occlusion is just wow, but I’m not actually sure about the difference of normal vs, bump those normal mapping change the direction a pixel is facing in any direction, instead of up just up and down, yup I’m a noob.
If you need to know, White = raised, black = lowered.