I didn't see any cap of how many points you can invest into one skill, but i've noticed that the effectiveness is reducing as you increase the amount spent. Like for the stunning skill, when you're upgrading duration, the first point increases a second, the second increases only 0,5 second, the third increases for even less... So it's just pointless after a while.

The only skill i've used skillpoints (or empower points or w/e you call them, you do know what i am talking about, sparky) up for is the Demoralizing Hit (or w/e), the one which reduces monsters' damage around the character (AoE).
I'm saving the points up for the AoE damage skills and defense buffs.

Btw, AndyB told me that the first AoE dmg skill (lv42 or 43, don't remember exactly) had a 20 second cooldown, so you won't be able to level with AoE-ing, it's much more like a "just-in-case" skill, at least until you get higher AoE dmg skills and reduce their cooldown with points.

max empower points we can use is 20 on a skill, 5 on each section,
-Effectiveness (damage usually, demoralizing hit increases the amount of def decreased; however it doesnt increase the strength of the "SIDE EFFECT" like reduced attack speed or reduced damage, those are set)
-SP Reduce (reduces sp usage)
-Buff time increase (this increases the buffs, debuffs alloted time)
-Cool Down Time Decreases (decreases the cool down time)

Someone else said this (forgot who this was), said the first point invested is the most amount increased then after that its just a little bit increased etc etc

How many aoe skill does a fighter have and what lvl does he need to get them??