The strikers present in the Fourth Edition Player’s Handbook are pretty straightforward. The ranger has hunter’s quarry, the rogue has sneak attack, the warlock has warlock’s curse, and they’re all pretty straightforward in their presentation: each one can only be used once per round to add damage.

Warlock’s Curse is probably the wordiest of the three, and is probably the most complicated, mechanically speaking. You place a curse on the nearest foe you can see as a Minor action, the curse remains until the end of the encounter, or the enemy is defeated, and while you can have multiple curses active, you can’t curse a foe cursed by another warlock (unless you have the feat — Accursed Coordination).

Sneak Attack is the simplest and most straightforward, as it states that hitting an enemy granting combat advantage with the appropriate type of weapon (why the weapon matters is beyond me) is enough. No matter how many attacks you get, or creatures you hit with a given attack, you only get the damage once per round.

Hunter’s Quarry is the second wordiest, after Warlock’s Curse, of course, and poses a dilemma: though it states that the damage can only be dealt once per round, it says so after it’s mentioned the limitation first in connection to hitting the quarry with an attack. Now, it’s stated later that you can only have one quarry at a time, so dealing extra Hunter’s Quarry damage in one round is practically impossible.

…Unless you’re playing a Battlefield Archer. One of the first abilities the Battlefield Archer (paragon path) receives, is the ability to designate the nearest x enemies as quarry. Due to grammatical tricks that can be played in the interpretation of the Hunter’s Quarry power, it’s possible to conclude that Hunter’s Quarry damage can be dealt once per turn, to each designated enemy.

It’s been a point of contention in our group for quite some time, but I think my most recent reading of the Warlock’s Curse has settled my mind. It’s possible for a Warlock to have multiple cursed foes, but they can only deal Warlock’s Curse damage once per turn. I believe this was also the intent of Hunter’s Quarry, even though the power itself is designed to only ever affect one target in the original text.

…In other words, you only get your Hunter’s Quarry damage once per turn, regardless of the number of creatures you currently have designated as quarry. You have to choose one, and only one, of your targets to apply it to.