I'm playing in one right now.
We're all githzerai, working on retaking the gith homeworld. Unfortunately, the entire planet is a wild magic zone, so everybody is psionic. We're gestalt as well, so the group has some fairly strange characters running around. There are a few gith subraces, as well, just so everybody's not the same.
We have about the same party roles as any other game, though. Things don't play all that differently. The GM added some healing stuff so that we could avoid dying all the time - essentially, the upgraded the Life mantle of the ardent in the group, so they could heal others. She has a healing-based PrC, as well. Otherwise, we're a pretty normal group.
Monk/Kineticist, our blaster. He's almost completely a psion, ignoring his monk abilities and focusing everything on psionic feats and such. He's quite effective at it, too, with more flexibility than most blasters I've seen.
Monk/Telepath. She's a melee combatant, mostly focused on avoiding damage. She's got an AC of 29 pretty regularly, at 8th level. She can dish out a fair amount, too, though her attack bonus is pretty poor.
Soulknife/Fighter, the one who doesn't like psionics that much. I think he's taken a level of psychic warrior by now, so he can use dorjes of Body Adjustment. He's a straight TWF warrior. Does a fair amount of damage, since he's got four attacks a round, all of them with a bonus damage die or two.
Fighter/Ardent, the group's healer. She has, I believe, the Life and Travel mantles, though I don't know if she's picked up more by now. She's got mostly empathic powers - in combat, she'll usually go melee (sword and board) and then use Hostile Empathic Transfer when she gets hurt. She's usually got a Share Pain up with a group member or two, as well.
Scout/Psychic Warrior, a skirmisher. She runs around the battlefield at high speeds, hitting people or shooting them with her bow. Not a lot of damage, but good for attacking casters and such.
Me, a Ranger/Psychic Warrior with a couple of levels in the Sanctified Mind prestige class, which is focused on killing psionic entities. I'm a beatstick, with a Vicious two-handed sword and the Great Cleave feat chain. Not a very good AC, but a lot of hit points and a really high Strength. I'm having a good time with it.