Some people don't like it, and only use it when really needed (i.e. generally only to remove medications), some swear by it, and there is that group of people, which i sit amoung, who like it for what it is, and use it in certain tanks which don't have plants, or fish which have a higher risk of getting hole in the head disease.
I use it in my main display tank, which has hardy plants, with my community fish. I believe activated carbon's benefits out-weigh its down sides (that it will remove some minerals, and absorb certain ingredients of liquid fertilisers, which i don't use on this tank).
My other tank is moderately stocked with live plants, and i fertilise this tank on a daily basis with liquid ferts. This is the main reason why i don't use activated carbon on this tank, and the other reason is it will possibly remove some trace elements or minerals which are found in my water supply which may be beneficial towards my plants.
-- Gomer
