FreeTheSlaves said:
The problem with any 3.0 haste-like spell is that it grants extra actions. Actions are a premium quality that can usually only be improved by having more allies on your side, allowing someone to improve their actions effectively increases the # of "allies" you have.
That's why I suggested the above. For a spellcaster the old Haste basically doubled your turn's worth of action. It is tactically a huge bonus, almost like having 2 spellcasters instead of one (almost but not quite, since there's still only 1 to kill

).
I don't know how to estimate the idea, but I thought that a good price for extra actions
now could be less actions
later. This could be a good compromise, as long as the duration is short enough so that almost always the price is going to be paid in the same combat. If the duration is 1d4+1, or perhaps 1d4 only, it's short enough that you run the serious risk of the spell wearing off before the end of the encounter.
Then the penalty kicks in for the rest of encounter and perhaps even longer. The key issue here is how to design the penalty appropriately. Something that would prevent spellcasting completely is IMO quite fair. We can considering the following conditions:
Exhausted: -6 Str and Dex (including weight capacity and AC) and half speed; takes 1 hour of complete rest to become Fatigued
Disabled (but not at 0hp): can only take partial actions, and standard actions deal 1 hp damage
Nauseated: cannot cast or attack, only 1 move action per round
Sickened: -2 attacks, damage, skill checks, saving throws
Slowed (as the spell): can take only partial actions, -1 attacks, AC and Reflex, half speed
IMO a good possibility could be that after the duration of Haste the character is (non-magically) both Exhausted and Nauseated for. The exhaustion works normally, i.e. goes away only on complete rest for 1 hour, then leaves the subject Fatigued only; it is a lesser penalty than nauseated, but still hurts. The Nauseated effect is IMO enough if it lasts for an equal duration as the Haste, either the same result or roll a different 1d4+1.