This is just my opinion, and I enforce it in my games, but I do not believe that psionics have a place in D&D. To me, psionics is a manifestation of an innate ability. The ability is derived from mental evolution of the race based upon solving more and more complex problems with pure intellectual might as well as an intense desire to affect the world around the individual and race. It is the result of a positive mutation. And the factors I feel are necessary to push the race into manifesting psionics is not present in the typical fantasy milieu of D&D. It just doesn't fit. It's like trying to introduce cattle ranching on the bottom of the ocean. Why develop a mental ability when you have the resources of clerics, druids, wizards, sorcerers, scrolls, wands, demons, devils, devas, genies, etc.?
Now, I've heard all the reasons and excuses for adding them. "A sufficiently advanced technology is indistinguishable from magic", as Arthur C. Clarke is attributed as saying. Okay, fine. Then psionics is just like arcane and divine magic. Just like it. Anti-magic shell stops it. Dispel magic stops it. Ring of Spell Turning reflects it. Rod of Absorption absorbs it. And I can already hear the screams of "But no! It's different!"
Fine, it's different. Explain to me how within the context of a fantasy milieu that a group of individuals developed a psionic talent.....in an area with gods, demons, and mages. Go ahead. You can't because it doesn't make sense in that context.
But I am perfectly okay with psionics in any other genre of rpg's. I think it works best in a SF setting in fact. Just look at Vulcans in Star Trek, Jedi in Star Wars, River Tam in Firefly, etc. It fits there. It's the "magic" of the system there. It just does not fit in fantasy.
That's my two cents on it.