I always like to dig into the how a game works, so I ran a few tests using the console. Had to use the console since we are still waiting on the Construction Set.

First Off - Power Attacks
ALL melee power attacks do double. Single sword or two handed. You will get a solid double damage. I have seen people posting that two hand does not get extra damage - but they do.

The stamina cost for one hand power attacks seems to be base 30 + 1.5 pts for each unit your weapon weighs. An Iron Dagger which weighs 2 pds will use 33 stamina and a Dwarven Sword which weighs 12 uses 48 stamina. A bound sword uses 30 points of stamina. So keep that in mind when looking at weapons damage - a lighter weapon will allow for more power attacks - which are double damage.

I am not sure on the formula for two hand weapons, still need to test more, but it is a lot higher then the one hand weapons. For instance an Iron Ax which weighs 24 requires 88 stamina to power attack! Yuck.

Now - the Bound Sword. Lots of people post it is a Daedric Sword. It is not even close. My Dwarven Superior Sword was hitting a little mage for 21. With a bound sword I was hitting the same mage for 15. Does not seem particularly powerful. Which kind of confirms my own in-game experience with the bound weapons. They are not that great.

For anyone on the PC who is interested in testing - use the commands - getav health to determine how much damage you are doing.

More important question: how do I do power attacks ? I do get them sometimes, but it doesn't seem consistent how to trigger them ?

I am dual-wielding swords.
I try to push both mouse-buttons at the same time. That seems to sometimes trigger a power-attack, but not always.
I also try keeping my one mousebutton (for the mainhand) pushed for ~ 1 second. And then release. That seems to trigger something some times too.

But I feel that I am completely missing the point.
What is it exactly that I should be doing ?

Did you have the perk that increases bound weapon damage?

To power attack when Dual welding - you have to hold down both buttons. You will get an animation that looks like you are hitting four times - an inside sweep followed by an outside sweep. But it still does double damage. Actually, *slightly* (about 4-5 more pts) more then double damage. All of the other power attacks do exactly double damage.

For th bound weapon tests I was using the bound sword with a 50 conjuration. Let me go add the Bound sword perks to see how it does.

Is this info correct how did you get it?

After raising conjuration to a 100 and adding every single conjuration perk in the game to my character the bound long sword went from 15 to 24 damage. This is with a One Hand skill of 39 and the armsman perk. My Superior Dwarven Sword was hitting for 21.

So overall, meh. I would pass on the bound items. Just carry a powerful sword as a back up, rather then wasting the perks here. Conjuration is still strong, just not bound weapons.

Also to recreate the tests I was using Ancano in the Mages guild as my test subject. Just use the console command getav health before and after your attack.