Buffs can't do damage. A buff is just a thing which is put on a player/monster and changes it's stats. A buff can't do something like react to you blocking and dealing damage out, the skill has to do that. Some skills create buffs, but they are not buffs themselves.
The passive skills which increase buff effect apply to all visible buffs (but not debuffs or charges) placed on your character - if it brings up one of those little squares in the upper left and it's good for you, then it will be affected. This includes such things as the buffs created by casting blood rage, phase run, and immortal call.
The passive skills which increase buff and debuff duration apply not to buffs on you but to buffs (including debuffs) you create, either on yourself or other entities. This includes all the above as well as such things as the debuffs placed on cursed monsters.
Skills causing buffs/debuffs (affected by both buff duration and skill duration):
- Blood Rage
- All curses
- Explosive Arrow
- Immortal Call
- Infernal Blow (technically, and likely to change - it affects the duration after the hit that they'll explode if they die)
- Lightning Warp
- Molten Shell
- Phase Run
- Poison Arrow (The poison debuff that the cloud puts on monsters)
- Tempest Shield
- Viper Strike
Note that spells which give you frenzy/endurance/power charges are not affected by these.
Passives
Basic Passives affecting Buffs are:
- Buff Duration (10%, 15%)
- Buff Effect (6%)
The Inner Force Notable Passive grants 18% increased Buff Effect.
The following is an excerpt from the PoE forums about how the "increased Effect of Buffs on You" passives work:
Buffs, in this case, refers to things that show in the top left of the screen, are not charges, and are not bad (those would be debuffs, these passive don't make those worse for you).The list of buffs affected by it is:
Aura buffs:
- All player aura skills
- All positive monster auras*
- Rejuvenation totem aura
Skills which make buffs:
- Blood Rage
- Righteous Fire
- Phase Run
- Tempest Shield block buff
- Molten Shell armour buff
- Immortal Call (technically, but being x% more immune is not noticeably different in practice)
Flask buffs:
- The three Resistance flasks
- Granite Flask
- Diamond Flask (see immortal call. x% more than all hits being crits is not a noticeable difference)