First off, I'm glad that there are spells that can actually create darkness again, rather than just create leaping shadows, but the revision of this spell causes me to ask a few questions.
On one hand, I understand that creatures like drow that cast darkness would potentially nerf their own allies when casting this, as it affected them all. I started using veil of shadows from the Miniatures Handbook for them to avoid this.
However, from an internal logic standpoint, why is this useful on most days for a drow or a demon, for example? Sure, drow and demons fight surface mortals from time to time, so this would be handy then. But most of the things that drow and demons run into on a day to day basis are creatures from the underdark or outsiders, beings that already have darkvision, meaning that most of the drow and/or demon's natural enemies are immune to this very common ability.
What I was thinking was that, perhaps, if this spell does create darkness that is negated by darkvision, what about the caster, if in range of the darkness, still retains concealment? If only the caster gains concealment when in the area, it doesn't hamper his allies, but it still gives him a benefit against even foes with darkvision.
My suggestion is have it create a zone of darkness that extinguishes nonmagical light sources. Darkvision still functions. This would hinder most surface races (only dwarves and half-orcs have darkvision), while not hindering casters with darkvision (such as drow). However, this effect may be more powerful than that of a 2nd level spell (compared to blur).