We use the XPH in our game and we love it. I also have Green Ronin's Psychic's Handbook and althrough I think it's an excellent book, as someone else said, it's more ideal for modern or another low magic/psionic world. The XPH just fits with D&D better.
We do use the psionics are different rules. I haven't encountered any major problems, though there's been some grumbling from my brother (who plays an evoker) that he always has to deal with spell resistance while power resistance has rarely come up for our friend who plays the telepath. Part of this is just that our group adventures in a region in which magic is far more common than psionics, and though the psion has gotten off easy on penetrating resistance, he also only has one psionic item while the party has found numerous magic items. At any rate, I'm about to throw some psionic duergar against them, and may put some mind flayers behind that, so the balance will shift back a bit. All in all, I'm glad we've kept the two power forms separate, and don't think the problems are too substantial. If your setting has magic and psionics both equally common there shouldn't be any problem at all.