Much has been said here about different types of curse cards. The main problem seems to be that a curse-with-benefit (e.g., Action-Curse, +3 cards, -3 VP) is actually a good thing on a board with trashing and brutal on one without. Furthermore, would the card cost something, in which case it just makes the card all the better in light of Salvager, etc, or is it free, allowing players to buy them on purpose for nothing? Someone in another thread brought up the point that such cards aren't really curses so much as negative victory cards.
But it occurred to me this would make an interesting Curse card with none of these problems:
Hex
$0 - Action-Curse
+1 Card, +1 Action
-2 VP
Setup: Place half the number of Curse cards in the kingdom as you normally would. Place an equal number of Hexes in a separate pile. When a player gains a Curse card, he may gain either Curse or Hex.
To balance the three-pile ending rule, it may be necessary to consider the Curse cards and Hex cards as belonging to a single pile.
I think this card is sufficiently useless as to qualify as a true "curse." It's admittedly useful in certain unusual situations (e.g., to help start a Conspirator chain), but then so is the regular curse (e.g., with Ambassador).
Yet this Hex card behaves very differently: At a greater VP cost, it won't consume a spot in your hand.
I suppose in a heavy-trashing game, you'd pretty much always take a Hex over a Curse. But otherwise it might be interesting to have to make the decision: Do you take the greater VP hit in exchange for a looser deck?