Maybe people are stepping on the bard's toes?

[Abraham spalding]

Just a thought but what does the bard have?

Buffing Music -- clerics get domain buffs (noble's even the same type)
Arcane spells in armor -- replacible with feats now
Jack of All Trades -- with rogue talents and higher skill points they've taken this roll. Heck wizards with their incredible Int bonus on ranks can almost fill this role better than the bard can! Especially when one of the bard's points is prespent on perform. Without cross-class skills costing extra the bard's list of skills becomes even more meaningless as it only nets a +3 on the skills he takes.
Spellcasting -- so what? every class except fighter, rogue, barbarian, and monk get this, and monk and rogue get some similar options. Multi classing can clear this up too.

Anything I've missed?

[KaeYoss]

Buffs: Of course others have buffs, too. Would be really weird if only bards could buff. Bards are still quite good at it, getting both class abilities and spells for it.

Armoured casting: Yeah, thereare feats for that. But they must be activated with a swift action, so you forego things like quickened spells if you choose to use them.

Skill monkey: Sure, the rogue gets more base skill points (2 more, or 1 if you count the knowledge skills from bardic knowledge), but bards will be able to make up for that in part with their intelligence - which is usually higher than a rogue's. And the wizard will have problems keeping up, since bards aren't stupid, either, and get a head start of 4 (or 5 if you count the bonus knowledge).

Let's look at things (not counting bonus skill points for being human or using favoured classes):

On 1st level

Rogue: Int 12 (probably won't have more, since dex and con are important), means 9 skill points per level (8 class, 1 int)

Bard: Int 14 (and that's a low estimate), means 9 skill points per level (6 class, 2 int, 1 bardic knowledge), with 1 tied up in knowledge skill.

Wizard: Int 18 (assuming you don't get a bonus to it and boost it to 20, but then again, a bard could do the same), means 6 skill points per level (2 class, 4 int)

Bard's actually tied of the lead, at first level. Later, the bard will probably get moderate increases to his int, and the rogue won't increase it, so he can pull ahead. The wizard will invest heavily into int, so he will probably get close, but not necessarily better.

On 20 level:

Rogue: Int 14 (just a minor boost from an item, and it's not unlikely that not even that will be taken), meaning 10 points per level now (8 class, 2 int), with one being tied up as a knowledge skill (from item)

Bard: Int 22 (+6 item, and 2 increases form level-ups), meaning 13 skill points per level (6 class, 1 bardic knowledge, 6 int), with 4 tied up in knowledge skills.

Wizard: Int 29 now (+6 item, 5 increases), meaning 11 skill points per level (2 class, 9 int), with 3 tied up in knowledge skills.

Not bad I'd say. And that's just raw skill points, bards do get a couple of perks here, over time: Take 10 on all knowledge skills, make knowledge skills untrained, Take 20 on a knowledge skill a couple of times per day, get a bonus to all knowledge skills equal to half his class level, use everything untrained, treat everything as class skill, take 10 on everything you have 5 or more ranks in... While right now, some of the best abilities I listed are granted on the penultimate level, Jason already mentioned that he'll probably make some of these abilities avaiable at a lower level (my suggestion was use untrained on level 4, gain all as class skills at 10, and take 10 on all at 19, and he meant that this is quite similar to what he was thinking)

I agree that 1-2 points per level are tied up with performance skills, but the bard is still quite the skill monkey.

Spellcasting: True, most classes have spellcasting, and bards aren't full-powered spellcasters like wizards. But it doesn't hurt, either. Plus, he has a trick or two up his sleeve no other arcanist can do.

One thing I'd like to mention is

Loremaster (though you could say this is part of skill monkey): With the bonus skill point, the ability to use all knowledge skills untrained, the bonus to all knowledge skills, the ability to take 10 (and sometimes 20) on knowledge skills, The bard gives the wizard a run for his money on this one.

Using the values from my skill point analysis above, A 1st-level bard will have a total bonus of +7 on his knowledge skills (1 rank, 3 class bonus, 2 int, 1 bardic knowledge), the wizard +8 (1 rank, 3 class, 4 int). On 20th, it's the bard's 39 (20 rank, 3 class bonus, 6 int, 10 bk) with the ability to make all untrained, always take 10 and sometimes take 20 against the wiazrd's 32 (20 rank, 3 class bonus, 9 int).

But what is it that lets the bard be the bard?

The answer to that is E) All of the above.

It's not about having something no one else has, it's about having lots of different talents no one can quite match:

A wizard is the better spellcaster overall, but the bard is more robust (better HD, ability to wear better armour without using feats and swift actions for it), probably as good a buffer (if not better) as the wizard, can heal people, and a decent enchanter and illusionist in his own right. The bard's better with skills, including knowledge skills.

The rogue is probably the better warrior, and in some areas the better skill monkey, but he can't heal, buff anyone, doesn't know anything and must rely on his skills when bards can use magic to charm and deceive

The cleric is even better protected (better armour, and tends to have better con), the better healer and better spellcaster overall, but the bard is still the better buffer I'd say, and with charms and illusions, as well as skills, clerics can't hold a candle to the bard.

I'd say that no one else can quite reach the mix of abilities a bard can achieve.