For my first post, I'd like to hear the edge-casers weigh in on when is a good time to buy (or voluntarily gain) a curse. I can think of two overall categories:
I) when a curse as such is the best card to obtain (voluntarily gain, or buy); and
II) when ANY zero-cost card (copper, curse, ruins) will do.
So here's my (hopefully not exhaustive) list:
Category I
1) to end the game on three piles
2) when Tortured
3) to deal out with Ambassador
4) to boost Fairgrounds
5) (much rarer) to boost Gardens
6) While possessing your opponent, use his +buy to get curses so that you can Watchtower them with your own hand and 3-pile
7)With watchtower in hand as the only trasher in the kingdom, buy the last curse so that your opponent doesn't curse you
8)In a draw-your-deck engine, workshop Curse to boost your Harvest
9) to deal out with Masquerade, when all the Masquerades are out (or maybe in some weird draw-your-deck/workshop/masquerade combo)
10) With Watchtower in hand as the only trasher and you know (via Bureaucrat or some such) that your opponent has a Mountebank in hand (so that you can top-deck the Curse and don't gain a copper as well)
11) When you know that your opponent has Sea Hag in hand, you can buy the last curse so that the curse goes to your discard instead of your deck
12) When you are ahead by a few points and one pile is already gone, to exhaust the Curse pile so that the opponent can't buy the last Duchy, Estate, or Alt VP card
Category II--(this will usually only happen if coppers (and ruins) are already gone)
1) With trader in hand to gain silver
2) When you have played multiple Goons (and coppers are out or you're trying not to 3-pile)
3) You know your opponent has multiple Goons and +action/+buy in hand, and the coppers are gone
4) When the coppers are gone and you play Haggler with no other cheap cards available
5) To add fodder for Junk Dealer or Rats (likely in a draw-your-deck engine)
6) With a Remodel type card, a draw-your-deck engine, and bridge/highway, to get a zero-cost card that can be then upgraded to the card you really need (maybe you don't want to lose any of the cards you already have)
7) With Watchtower in hand, to trigger Market Square
I've tried to think of all of the edge cases, but I'm sure there are many more. Any suggestions?