Henry said:
All of the spells mentioned by the others (The power word spells, Otto's Irresistable Dance, etc.) have one thing in common - they are 8th or 9th level in power, and meant to be cast by hideously powerful spellcasters against hideously powerful opponents. Power word Stun does not make an opponent helpless, but it does give you an advantage for a couple of rounds.
Harm is a 6th level spell, and deadly to most living beings. Against anyone but the exceptionally swift, it is a combat-winning spell, castable by someone just halfway to maximum level.
I am not very familiar with the spell list myself as I tend to not play spellcasters, but here is a quick observation I made...
Flesh to Stone is a level 6 spell for a Wizard/Sorcerer. Compare this to Harm now.
Stone to Flesh doesn't technically kill the opponent, but does turn them to stone (permanently I think). I suppose you could knock their head off after that. STF doesn't require a "to hit" roll, and has a range of about 100+ feet. It doesn't have to hit an AC, but a Fort save is required. You could enhance this with feats to help it penetrate the Fort save (Heighten spell, Spell Focus, Spell Penetration, etc.).
Harm also doesn't technically kill an opponent, but it does render them to 1d4 hp, which is good enough. Harm doesn't have a save attached to it, but you DO have to get within range and make a melee touch attack on the creature to hit. You could enchance this with feats, such as Reach spell (makes it a 30' range touch attack) but that would also up the level.
I think these two spells are very similiar in a lot of ways. Neither outright kill the opponent. Both require some sort of roll to effect the target (one a melee touch attack, the other a fort save). One can be used at range (which makes it easier to land) and one has to be used in melee (which makes it more dangerous to land). Both can be increased in power using feats. Oh, and one more thing... If the target of STF is effected, they can not do anything to get out of the effect (aside from a Contingency). If they are hit by Harm, they are still alive enough to do something (heal themselves or otherwise escape).
So, is Stone to Flesh over powered too? If not, why? They seem very similiar to me, they just use different mechanics to produce the same type of effect. Except STF has two benefits to it that Harm doesn't, it has range and once you are affected by it you are stone whereas with Harm you have a chance to react (depending on initiative and what not) because you are still alive for a moment =).