To begin, let me state openly that I really like the idea of using Turn/Rebuke attempts to add longevity to a group's adventuring. Having to rest for a day after every significant encounter can really suck so anything that helps to shore up a group and get them back in the fray is good in my book.
Having said that, evil clerics get the shaft. Unless they are undead themselves, it could be argued that they will be damaged by their own Rebuke attempt. Even if that is not the case, a cult of evil clerics attempting to bolster their undead followers is going to decimate itself when Evil Cleric A attempts to Rebuke and also hits Evil Clerics B, C, D, E, and F. And when each of the Evil Clerics A-F all attempt to Rebuke, they end up as smoking piles of ash consumed by the negative energy of each others' Rebuke attempts.
Even without there being a group of evil clerics, putting the adventurers (presumably goodish) against an opposed evil group with a cleric tips the advantage unfairly in favor of the adventurers because the evil cleric can't use the same abilities available to the good cleric without harming his own group. The good cleric can just position himself 30 feet from as many of his allies as possible while staying 35 feet or more from any enemies and channel positive energy in combat as a healing boost to augment his other curative abilities.
Part of the problem here is that the rationalization is based on the positive/negative energy paradigm. If it were changed to some other function that converted Turn/Rebuke attempts into a bolstering effect for allies, then it would be equally useful to both sides. It would be similar in concept to the many and varied feats that convert Turn/Rebuke attempts into everything under the sun and could be introduced as a free feat to Clerics and Paladins as well as other classes that are able to Turn/Rebuke.
Anyway, that's what I think.
Unless they are undead themselves, it could be argued that they will be damaged by their own Rebuke attempt.
In the second paragraph below the heading 'Rebuking Effects' it states "You can choose whether or not to include yourself in this effect."
Even if that is not the case, a cult of evil clerics attempting to bolster their undead followers is going to decimate itself when Evil Cleric A attempts to Rebuke and also hits Evil Clerics B, C, D, E, and F. And when each of the Evil Clerics A-F all attempt to Rebuke, they end up as smoking piles of ash consumed by the negative energy of each others' Rebuke attempts.
This is actually kind of flavorful for an evil cleric. They are eeevil after all. Harming their living allies (and opponents) while they bolster their undead minions seems like the kind of trade-off an evil cleric would make.
Still, you're right, there is a balance issue there. I'd suggest as a possible fix, altering the AOE from a 30' burst centered on the cleric to a 30' cone. This would allow clerics to use the turn/rebuke more tactically, and give Paizo a reason to commission a new pair of effect templates from Steel Sqwire. Hell, I'd buy 'em.
Even without there being a group of evil clerics, putting the adventurers (presumably goodish) against an opposed evil group with a cleric tips the advantage unfairly in favor of the adventurers because the evil cleric can't use the same abilities available to the good cleric without harming his own group. The good cleric can just position himself 30 feet from as many of his allies as possible while staying 35 feet or more from any enemies and channel positive energy in combat as a healing boost to augment his other curative abilities.
Part of the problem here is that the rationalization is based on the positive/negative energy paradigm. If it were changed to some other function that converted Turn/Rebuke attempts into a bolstering effect for allies, then it would be equally useful to both sides. It would be similar in concept to the many and varied feats that convert Turn/Rebuke attempts into everything under the sun and could be introduced as a free feat to Clerics and Paladins as well as other classes that are able to Turn/Rebuke.
There are already a ton of feats in D&D 3.5 that do convert turns to do other things. Unfortunately, some are subjectively useless and others are extremely overpowered. (Divine Spellpowered Holy Word/Blasphemy anyone?) I do like the idea of either separating the healing/damaging aspects to the effect, or perhaps making them alignment dependent rather than flat positive/negative energy. By separating them, a positive energy cleric could choose to heal his allies OR deal damage to the undead while an negative energy cleric could heal his undead OR damage his allies.
Making them alignment dependent, the good clerics turning effect would heal good characters and deal damage to undead, and the evil cleric could deal damage to good characters and heal the undead. Neutral characters could suffer a lesser effect (half damage before the save, or half the healing rolled). Of course, neutral positive energy clerics would kind of get the shaft, as their own positive energy would only heal them half as well as their more pure allies.