One of the benefits of the Dark Creature template (Tome of Magic, p. 161) is that you get +10 feet "to all modes of movement".
Let's say I take a level in Ape Totem Barbarian, which grants a climb speed "equal to one-half his base land speed". Will the Dark Creature's effect apply retroactively to the new mode of movement? In other words:
Dark Human: 40' base land speed (a) Climb 20' (one-half BLS) (b) Climb 30' (one-half BLS + 10' from Dark)
Is (a) or (b) correct?
Now what if I'm just a normal human, take that same level in Ape Totem, then don the Collar of Umbral Metamorphosis (an item which bestows the Dark template)? Will my climb speed be
(a) Climb 25' (fixed at one-half original 30' BLS + 10' from Dark) (b) Climb 30' (one-half new 40' BLS + 10' from Dark)
The first instance is a question of retroactive application, the second a question of re-calculating values (does the "one-half base land speed" recalculate, or stay at the value of its initial calculation?).
As an aside, I assume that haste would work similarly to the second example.
Edit: Haste doesn't alter "base" speed like the Dark template does.