Pacifist: How feasible is it?

[Callista]

I've been poking at the idea of playing a character, probably a wizard or cleric, with Vow of Nonviolence or maybe even Vow of Peace.

Assume that I'd be playing this in a group where it wouldn't be a drag on the rest of the party (i.e., mostly Good and willing to solve things in non-violent ways, probably heavy RP, strategy, diplomacy and skill use).

How feasible is this, mechanically? Does a spellcaster really suffer all that much from refusing to cause harm to others?

If I actually go for Vow of Peace, is there a foolproof (or mostly-foolproof) way to hold a prisoner--humanely--without worrying about him stabbing me in the back in the middle of the night? Would it be considered "damage" to petrify and Shrink Object on a prisoner, if I also had the requisite Break Enchantment to safely restore him?

My group usually optimizes pretty competently, so I need to make sure I can stay at a similar power level. I like this concept; I'm getting bits of backstory that keep popping into my head and I really want to try it. But there's no sense in role-playing a character who'll either be useless or annoying or die in the first battle, so I need to know if I can really do something with a pacifist character, or if it's too much of a handicap.

[IthroZada]

A Beguiler might pull it off as well... A Rainbow Servant Beguiler could do real well. With the wizard, you can just straight up ban the evocation school and the Cleric could possibly focus on buffs. A War-weaver might be nice too, when thinking about buffs.

Edit: And the Beguiler gets a wonderful amount of skill points for that Diplomancy.

[Epsilon Rose]

It depends a lot on the campaign your in (what are you fighting, why are you fighting, ext), your party (not just if they're good, but how patient they are) and your DM (if he allows Diplomancy then you're set, if he things the npcs [especially the important ones or the ones fighting] you are going to act a certain way and that's that then you're in for a ruff ride).
Generally, I wouldn't expect it to work well because 1) if a single character is talking everything into submission then the rest of the party isn't doing much and it gets a bit boring and 2) combats expedient and efficient, it doesn't require long negotiations or risk a double cross and lets face it, it's fun.
If this is an incredibly social game with lots of intrigue where actually fighting things is purely optional then pacifism is valid, otherwise you'll probably end up as a pacifist in name only.