Some (I would say many) BoED spells and items are underpriced, overpowered and/or too low level (for spells).
Lots of large radius area spells that blind/nauseate/xxxx all evil creatures. Same spells also deal 1rnd/level damage to the same area. And the save only helps for the blindness/xxxeffect etc.
I just have had an idea to give few of those spells to my players as special end-of-adventureseries prices. Our game is bit munchkin, and still I have raised the levels and removed some abilities of the spells.
Some examples are Empyreal Ecstasy, Ember rain, Righteous Smite and Rain of Black tulips. Those are ok with some tweaking and such.
There are others with even more power. Of course, they are hard to get or have some limitations who can cast them or they have some have ridiculously steep costs for casting. (Pay 1 level for few summon monster IXs or 40d6 area damage? Yeah right
)
I do think BoED and BoVD should be totally DM eyes only. The prestige classes, spells and magic items are not too well balanced. Good DM can give some things as treasure or abilites, but should do so only with great consideration.