I'm currently playing a lvl-5 psion, Sabat, who I am enjoying immensely.
I am having some difficulty in combat, but I am able to contribute. With Empathic Transfer, I can heal more damage than the cleric can do in a single round (even though I have to heal myself afterwards). We have 7 players, so it's usually not difficult for me to hang back from combat if I have to (although I never do

). I can use a mace and shield without trouble (and since it's a mithral shield, I don't have to worry about the armor check penalty). I'm a Shaper, so I can manifest Astral Construct II to fight for me if need be. And, once I hit 6th lvl, I'll be able to create tatoos for the party, which are much nicer than potions (no weight, no vial to destroy).
I already have plans for large damage powers. First of all, Metaphysical Weapon/Telekinesis can be a nasty combo. Whoever wrote Telekinesis must have been asleep at the wheel, since they never specified a limit to the number of items that could be launched. However, I worked out a house rule with my DM, and he's limiting the number of objects in the violent thrust to be equal to the psion's Intelligence score. So, manifest Metaphysical Weapon on 20 crossbow bolts (which do 1d3 dmg as a melee weapon), then toss them at a target for a potential of 20d3 + 60 dmg on a single target. KABOOM!
Greater Biocurrent is a great damage power, too. And, I'm working on a Telekinetic Maelstrom power, which will do AoE dmg over several rounds (subject to Concentration checks), so in the long run I doubt I'll feel underpowered.