I'll preface this by saying that I haven't playtested Pathfinder, so I apologize in advance. Unfortunately, I'm not in any gaming groups right now, so I can't put the rules through their paces. That being said, I can't in good conscience let the Bard's Deadly Performance slip through without comment.
This looks like one of the most over-powered abilities I've ever seen on a class.
Deadly Performance (Su): A bard of 20th level or higher
with 20 or more ranks in a Perform skill can use his
performance to cause one enemy to die from joy or sorrow.
To be affected, the target must be able to see and hear the
bard perform and be within 30 feet. To use the ability, a
bard makes a Perform check. His check result is the DC
for each affected creature’s Will save against the effect. If a
creature’s saving throw succeeds, the target is stunned for
1d4 rounds and the bard cannot use deadly performance on
that creature again for 24 hours. If its saving throw fails,
the target dies. A bard can use this bardic performance
ability utilizing any type of Perform.
Let's look at what a typical 20th level Bard can do, without magic items or spells.
23 ranks (+23 modifier)
22 ability (+6 modifier)
2 Masterwork instrument (+2 modifier)
For a total of a +31 modifier. With the Jack-of-All-Trades skill he can take 10 on his Perform check. This means that the Bard can throw around DC 41 save-or-die spells every round. And he can do it for 20 rounds. I didn't even factor in bonuses the Bard might have from Skill Focus, magic items, or spells. At 20th level, it would be very easy to up the DC to 50+. I don't know of a single CR20 monster with a Will save of more than +25 or so. That means that this ability has a 95% chance of killing anything the Bard targets. 20 times a day. And it's not affected by Spell Resistance.
I can understand the desire to give the Bard something special, and powerful, but this is overkill. I would strongly suggest detaching the save DC from a Perform check, in order to bring it back in line with 9th level spells. Perhaps even make it more like Phantasmal Killer, since the Bard can use it so much more frequently than casters can cast their 9th level spells. Or make it cost 4 uses of Bardic Music. Or something.
If I've missed some critical limitation to the Deadly Performance, I apologize. As far as I can tell, this is broken.
I would agree with this if the Bard can use this ability during combat. If the target is distracted, even a little, by other things going on, I'd say this ability shouldn't work.
And given the above, when would you use it? The Bard gives a performance for the evil king and... kills him with sorrow?
Granted, I don't much like Bards, but this ability just seems a bit off.
I love the bard, and even I think Deadly Performance is way, way off. Fortunately, we have it confirmed that it has been changed for the beta, so I'm going to wait and see that until I comment on it further.