Most of your non-signature attacks that deal damage will consume the effect but you have to build up 5 stacks first.
It is an additional 75% so it will scale with the damage of the secondary attack used: the higher the damage of the spell used, the more noticeable it will be.
If you build up the 5 stacks then cast something with large amount of damage (non-channeled and non-DoT are the most noticable) like Arcane Orb you can see a large increase in the damage.
You can turn on the display of damage in the options screen if it isn't on and it will show the numbers.
DoTs - It does work on DoTs (Venom Hydra, Blizzard, etc). Increases the amount of all ticks, not just the first one.
Channels - Works on channeled spells (Disintegrate, Ray of Frost, etc). Increased for the whole duration of channeled spells. Some
people have reported a drop off in damage after the first few seconds on Disintegrate but I haven't seen this.
Archon - It does work but only increases the first attack and not the whole duration.
This is based on my own testing and the general consensus for what I've read about it.
Edit: Here is a spreadsheet someone put together showing the damage increases for most of the spell/rune combos: