Curses aren't usually a problem when my group plays Dominion, there's a sort of unspoken gentleman's agreement not to bother with the Witch. As far as attack cards go the Witch IS kinda lame imo, +2 cards isn't that special when the spy can be played literally for free, the militia gives you cash, and the bureaucrat gives you reusable cash. Thieves aren't always as practical, but work pretty well depending on the other cards in play (Money Lender, for example). All that makes it easy to ignore the Witch.
When we HAVE seen curses take a starring role, two of us started buying and using witches and defending against each other with moats, while the third player - who had missed the opportunity to stock up on moats - just eclipsed the curses by buying victory points and ended up winning the game. Fighting so often fails the combatants and benefits neutral parties...
I tend to prefer if no one bothers with her though, I just don't like the card. I don't know why a single action card requires an entire special deck to be in play, I would rather they spent the space in the box with more unique action cards.