I only put a small number in any campaign, perhaps one every 5-7 levels. I like to include quirky items though, like a recent suit of armor that I gave out. It's encrusted with salt. The salt wears off over time, so you have to go dunk it back in salt water again. But while it's encrusted, it gives you a Swim speed, even in fresh water. I also gave out Venombrawn, a sword that makes the wielder stronger when they get poisoned (which led to much hilarity where my giant akashic has been figuring out how to poison himself).
By far my most fun cursed item was the Staff of Curing. Just like a normal First Edition D&D staff, except that you had to hit someone with it to heal them. Do 1d4 damage, heal 1d8. It worked out on the plus side for the most part. However, there was one scene where the cleric kept whaling away on the fighter, doing slightly more damage than he healed every time, until someone else made him stop.