Since no one's mentioned it: Psychic Reformation (p127) seems ripe for abuse.
What it does is let you re-pick feats, skill points and powers. It costs 50xp per level you have to go back to (so if a 10th level character wishes to change a feat selected at 6th level, it costs 200xp). This cost is split between manifester & subject. You can change all of the feats, skills and powers selected back to the level you've paid for (so the above 10th level character could also change an 8th level feat pick). The only restriction is that you have to qualify for feats normally (so your 6th level feat re-choice can't require a +8 BAB for instance).
The abuse? consider a psion who at 6th level picked Weapon Focus as a feat, and decides that was a mistake. At 7th level, she picks Psychic Reformation as a power. Now, she expends 100 xp to allow here to change here 6th level feat. But, after she does so, she'll no longer need Psychic Reformation! so, she also re-picks PR! Meaning, that at any level that a Psion, Wilder, Erudite or Psychic Warrior can aquire a 4th level Psion/Wilder power (and all of them can, via feats if nothing else) they can re-pick as many powers, feats and skills as they are willing to pay xp for! And they don't even have to keep PR as a power, since they can also re-pick it at the same time!
A secondary abuse also exists for Permanancy: Since Psions always gain 2 powers/level, they can pick (starting at 9th level) both Permanency & PR; then they can manifest Perm. a couple times. Then, for 50xp they can re-pick both powers!
I'm not sure what ought to be done about this; maybe make it so PR can never re-pick itself? that would still leave the Perm. abuse, although it's not nearly as bad then; it would in effect cost 50xp to temporarily possess Perm.