Ath'kethin
Elder Thing
Meh, if you spent 40 PSPs on a disintergrate attempt at low level, you were pretty much done for the day.
Psionicist: "I summon all my inner strength to rip that Ogre apart with the power of my mind"
DM: Rolls dice "The Ogre feels a slight tingle and not much else"
Psionicist: "Sorry guys, I'm all out for the day."
It made them different from Spell Casters that they could throw their entire reserve into a single power.
In fairness, the inability to run out of spells/powers for the day is new to the game as of 4e.
And not to nitpick, but in 2e psionics the player generally rolled the dice; the powers were essentially skill/ability checks, with extra effects if you rolled the exact number you needed for the power to work.
And the game has plenty of "potentially blow your spell" type effects now; flesh to stone, for example, has no effect if the target makes its save.
Come to think of it, I also think that the tension of going for broke in using a power made for some pretty memorable scenes back in the day, too.