One of the differences between 4e D&D and other editions is the elimination of penalties. Everything is expressed as a positive. Rather than suffer a -2 penalty to your AC when you’re prone your opponents receives a +2 bonus to attacks made against you because you’re granting combat advantage. Sure it’s the same thing, but there’s a lot to be said for keeping things positive. With all modifiers expressed as positives, it’s up to the attacker to keep track of them and add them when appropriate. This makes things a lot easier for everyone since you know that none of your defenses will ever get lower. Your AC of 15 remains an AC of 15, even if you’re prone.
By eliminating penalties and negatives from D&D, curses – especially cursed items – have disappeared from the game. We no longer have cursed items in the traditional sense because they’ve always imposed negative penalties. Where a normal magical +1 sword provides a positive modifier, a cursed weapon (or a -1 sword) imposes a -1 penalty in much the same way. But since 4e D&D doesn’t have negative modifiers this kind of item doesn’t really work in the way that it did in previous editions.
Just because the mechanics don’t easily support permanent penalties, curses and cursed items shouldn’t be eliminated from D&D. There are still a lot of good ways to introduce curses and use them in you game. However, instead of imposing a mechanical penalty like -1 to attacks made by the poor PC unfortunate enough to grasp the cursed weapon, think bigger and apply the “penalty” in a more abstract way.