geosapient said:
I would have thought that the critical mechanic for this would be like multi-shot (can't remember if this is the actual feat name). You use one attack roll for every arrow that's fired and if the roll is critical then only the first arrow does critical damage.
The only real difference is that now you're hitting (or missing) multiple targets so the first one in the attack should be designated.
You mean Manyshot: From my version of the SRD
Benefit: As a standard action, you may fire two arrows at a single opponent within 30 feet.
Both arrows use the same attack roll (with a -4 penalty) to determine success and deal damage normally (but see Special).
For every five points of base attack bonus you have above +6, you may add one additional arrow to this attack, to a maximum of four arrows at a base attack bonus of +16. However, each arrow after the second adds a cumulative -2 penalty on the attack roll (for a total penalty of -6 for three arrows and -8 for four).
Damage reduction and other resistances apply separately against each arrow fired.
Special: Regardless of the number of arrows you fire, you
apply precision-based damage only once. If you score a critical hit, only the first arrow fired deals critical damage; all others deal regular damage.
The bolded part talk about rolling once and precision damage. Whirlwind Attack does not have these notes.
5 foes = 5 attack rolls.