CRB:
Countersong (Su): At 1st level, a bard learns to counter magic effects that depend on sound (but not spells that have verbal components). Each round of the countersong he makes a Perform (keyboard, percussion, wind, string, or sing) skill check. Any creature within 30 feet of the bard (including the bard himself) that is affected by a sonic or language-dependent magical attack may use the bard's Perform check result in place of its saving throw if, after the saving throw is rolled, the Perform check result proves to be higher. If a creature within range of the countersong is already under the effect of a noninstantaneous sonic or language-dependent magical attack, it gains another saving throw against the effect each round it hears the countersong, but it must use the bard's Perform skill check result for the save. Countersong does not work on effects that don't allow saves. Countersong relies on audible components.
Observations:
Perform can be used untrained. So any Bard who has the countersong class ability could make a check.
[Table: Skill Check Bonuses
Untrained Skill Check = 1d20 + ability modifier + racial modifier
Trained Class Skill = 1d20 + skill ranks + ability modifier + racial modifier + 3]
Questions:
If the opponent goes in the surprise round, can the Bard attempt a countersong?
If the opponent goes first in the initiative order, can the Bard attempt a countersong?
If the Bard has already used his actions first in the initiative order, can the Bard attempt a countersong?
If the Bard already has up an ongoing bardic performance (e.g. Inspire Courage) that uses one of the countersong skills, can the Bard attempt a countersong?
Is a Spellcraft roll required to determine that a countersong should be executed?
If a Spellcraft roll or a readied action is required to use countersong, it seems a very weak ability.
Against a Banshee, the Wail is a level 9 spell and the Banshee has Charisma of 19 = +4, so the DC is 10 + 9 + 4 = 23 [Fortitude as laid out in the Banshee entry in the Bestiary 2].
If the Bard has a +22 to one of those Perform skills of countersong (with the assumption that a 1 on the d20 isn't an automatic failure since this is a skill check), is a roll even needed for anyone in the party?
Activating a countersong is a standard action. This means it can't be made reactively to quickly counter an enemy action, as you seem to think.
If you're up against something that you know uses audible attacks, like a Harpy, you activate countersong preemptively. If a spellcaster surprises the party with an audible effect, then you can activate countersong retroactively to gain an additional save.
It's not a great ability, but it has its uses.
Is a Spellcraft roll required to determine that a countersong should be executed?
Probably not. You can't use Spellcraft against supernatural abilities like those of a Harpy anyway, but a Knowledge skill could help you tell whats going on. Though you should probably be able to guess that anyway.
IIf the Bard has a +22 to one of those Perform skills of countersong, is a roll even needed for anyone in the party?
Since it's used as a save, it's possible that a natural 1 should still be considered a fail.
Now that I read further up the page in the CRB from Countersong, that ability is in the section on overall Bardic Performances. It sure seems that at level 7, the countersong could be started as a move action, and at level 13 as a swift action (assuming you get the initiative and find out enough from a knowledge check to figure that you need a countersong). This also seems that you could do the switch of performances as a move or swift action at the appropriate level.
Readying an action is standard, so you could start Inspire Courage as a move action at level 7+ in the opening round, perform a knowledge check to determine the special attacks of the enemy include a sonic attack option, and then ready the Countersong in case a sonic-based attack is launched.
Of course, without any suspicion of a sonic attack, and getting surprised or losing initiative would still prevent the countersong in case of an instantaneous effect.
For the switch of performances: at your turn, free action to drop the Inspire Courage, and move action (at level 7) to start Countersong. You can have a bardic performance up constantly, until you run out of rounds.
I am with you on not needing Spellcraft. Using an appropriate Knowledge check against the monster would be the more likely route to take to determine that beginning/readying a countersong is the best course of action.
There isn't anywhere in the Countersong description that talks about a natural 1 meaning anything, and we know that for general usage of performance skills, a natural 1 does not mean any ill effects. I grant you that this makes Countersong better in at least one respect than an actual saving throw, but really, the related performance skills are easier to boost than any saving throw. So, short of having to wait around with a readied action, and having to drop the Inspire Courage or other performance as a free action on your turn, the actual numbers on the countersong should be impressive as a substitute save.
On rereading the Perform skill description though, it does say that you need at least 1 actual rank assigned for some tasks. "Trained: A bard must have ranks in specific Perform categories to use some of his Bardic Performance abilities."
However, neither Countersong nor Distraction say you have to have ranks, just that you must be using one of the specific skills.
"Bardic Performance: A bard is trained to use the Perform skill to create magical effects on those around him..." This does not strike me as actually requiring ranks to do Countersong or Distraction.