Does this perk only count for power attacks or regular attacks aswell?

It will speed up both, if i'm not mistaken.

IIRC It's regular only.

I like dual flurry a lot. Do you sometimes feel like you want trade some protection for extra damage? How would you like 35% more damage for the cost of 50 Armor protection? Wait there is more. Do you enchant your weapons? This 35% damage improvement not only improve the physical damage of your weapon like armsman, but also multiplies damage done by your enchantments.

This is what dual flurry does. You put away your shield and you gain attack speed. Attack speed = more damage.

Aight, i'm using 2 maces and want more attack speed for normal attacks. I tryed yesterday with 1 point invested in Dual Flurry, but can't really say there was any difference i could be wrong though.

Two maxes will always hit hard, but slow. Never been able to get them to speed up a "decent" rate. They do move faster with dual flurry, that I can vouch for.
If you are looking for something a bit faster that still packs a punch, what I did, and was quite pleased with was dual wield axes. I love the skyforge war axe, but fell free to pick your own favorite out and try them out!
If you still want to use a mace, try the old dagger in the off hand trick. By off hand, I mean left hand. Happy smashing

Are you power attacking all the time? I'm not sure, but I think perhaps dual flurry does not benefit power attack too much, because there is that recovery time after you attack. Try regular swings with just the main hand. Well, that's what I do. If you are power attacking, then what you need is the dual-savagery perk, for extra damage.

Dual wielding confuses me, because it is DUAL wielding, the art of using two weapons, yet this perk benefits you more if you just use your main weapon? Why not just have this ability for one weapon as well?

The difference when dual wielding swords is huge. The standing power attack goes very fast, you can just rush in and kill just about anything with it.

Dual wielding is WIELDING two weapons. You don't have to use them both to get benefit. I think most people do dual wield mostly for dual power attack, like the forsworn briarhearts. But you still get great benefit out of dual wielding for one handed regular attacks, which is what I use it for mostly.

Are you dual wielding Daggers? Because the Standing Power Attack for dual wield daggers is slower than Power Attacking with other weps, due to the animation of flipping the knife over in your hands.
Pms00 goes pretty in depth about explaining it. http://www.youtube.com/watch?v=GJEdi2WzkLc