Understanding the fine print for blindness
Solution 1:
As far as I've seen (playing a Guardian and a Thief both based on some Blind) I can answer you:
1) An attack is a single strike or a single projectile or something like this, something that can miss and that triggers "attack effects".
2) Hundred blades inflicts 8 attacks, so the first one misses for Blind purpose, while others will go on target, unless the Blind source comes from a renewable source, like a field.
3) A meteor shower actually throws lots of attacks, notice how you could, with some luck, pass it unharmed if you manage to avoid the single meteors, so the first one hitting a target should miss, ending the blind effect (must try with my Elementalist, now that I think about it), while a frost or poison field is not really an attack itself, it doesn't make attacks, you trigger their effect by walking into them, so they are unaffected from Blind.
4) The Thief sample follows the same rule for condition fields, if it's the field "activelly" trying to hurt you (like a meteor shower, again) it is affected, otherwise it works normally, notice that the Blind condition doesn't prevent the attack to start, it prevents the attack to hit, so attacks which don't follow a hit/miss rule are not affected from Blind. Being the field normally created, combo skills will also work.
Again, this answer is based on my experience being sometimes the inflictor of Blind, and sometimes the one who get blinded. Hope this helps.
EDIT: For pulse AoE the Blind condition negates the first pulse for every foe on the AoE, but other effects and subsequent pulses will work as intended.
EDIT2: Of course, if the AoE is compose of a single hit, it will miss completely due to the Blind condition.