IO stats: What do they mean?

I was looking at the Mako line and wondered about the "Chance for lethal" does that apply to just that power I slot with it or does it apply to all power once slotted in one, and is it worth it? Also the Damage buffs by X%, what exactly does that doe for you?

The Chance for Lethal applies only to the power it is slotted in. It gives a 20% chance of applying additional lethal damage when the power successfully hits. It is best used in a power that recharges and animates quickly. So, if you have a Katana scrapper you would want to put it in Gambler's Cut or Sting of the Wasp rather than Golden Dragonfly.

The Damage % (in Mako's case 3%) is a global buff. If you have 4 or more Mako's IOs in the same power all of your attacks get a 3% damage bonus added to them.