Playability of Ability Score Damage !?
While I enjoy 3E a lot, I fear no game designer considered the consequences of ability score damage (especially temporary!), which comes from e.g. poison or psionics.
This temporary ability score damage isn't easily managed. Just look at the CharSheet and consider the places where Ability Bonuses are calculated into the effective bonuses - there are a lot! And then you get into some psionic combat or get poisoned and you suddenly have to recalculate your effective skill bonus, AC, Saves, hit points and anything else which depends on an ability bonus !?
While it might have been an obvious choice at the first look, temporarily losing ability scores turns out to be unplayable, I fear (while it may be a good rule for a computer-based game!)
Losing ability scores sometimes is a nice effect - if the amount doesn't change all the time (like an effect of a curse, which is in effect and that's it; or even a spell that boosts one of your scores). But think of the effects of psionic combat ... 5 different attack modes, each damaging a different ability score ... and the amount of damage is likely to change every round ... ts.
And about psionics in general: With the introduction of 3E the game system was streamlined and simplified a lot (it isn't called "d20" just for fun - remember

?) ... but why wasn't it possible to just add a Mental AC, Mental Hit Points and a Base Psionic Attack Bonus? It would have been much simpler ...
When 3E was designed, the designers decided to only keep the "holy cows" as guaranteed unchanged, but who told them that the 5 psionic attack and defense modes were holy cows? They even got rid of the "Sciences and Devotions" of 2E and introduced 9 power levels just like with the spells, so why keep those old attack/defense modes?