Some effects key off of damage "dealt", such as Hellcannon Reserves. However, a few cards have wording that speaks of "taking" damage, such as Arrer Boyz and Beserk Fury. What's the difference, if any? Berserk Fury states that the target unit gains 3 power until end of turn, at which point that unit TAKES 2 damage. Since it doesn't say the unit is DEALT damage, does Berserk Fury still cause two damage with a Hellcannon Reserves in play, or does the TAKES clause not matter and the Reserves increase the damage from Berserk Fury to 3 (as it is a tactic)?

In a different scenario, there is a copy of Arrer Boyz and a copy of Big 'Uns in the same battlefield. The Boyz are activated once and deal damage to a unit in a battlefield, and then TAKE (according to the card text) one damage themselves. Then, the same Arrer Boyz activate their action again. Since they already sport a damage, they have Toughness 1 from the Big 'Uns; does this mean the damage they TAKE from the second use of their action is canceled when assigned like in most cases, or because the damage is TAKEN and not DEALT, is there no damage ASSIGNMENT, and therefore the toughness 1 does not prevent it?

I felt clarification on these issues was becoming more important now with cards like Bloodletter being released.

The FAQ doesn't really seem to explain it outright, but from what I've seen on the cards, 'take damage' is used predominantly when the unit would be dealing damage to itself. As such, it should be treated like any other damage, and Hellcannon Reserves would not chip in, because it's not the tactic that's doing the damage.

I could swear I've seen the damage dealt vs taken explained somewhere that looked official, but for the life of me I can't find it.

"Take damage" simply means that the unit itself is the source of the damage it is being dealt, nothing more. See http://www.fantasyflightgames.com/edge_foros_discusion.asp?efid=154&efcid=4&efidt=282587