What makes a good icon?

oreillynet.com - Jon Hicks, creator of the Firefox icon sounds off on 'what makes a good icon':

"That's a really hard one to answer, but I guess it all comes down to simplicity that can work at small sizes, and still have scope for detail at large sizes... Basically there are two aspects that are the base of a good icon: 1) shape, and 2) use of color. If you look at the Appzapper icon you will see that it 1) has a original shape, and 2) uses irregular colors and an irregular color combination. Doing a blue circle will not stand out...

I guess there are two extremes in icon design; foto realisme (Aqua) and abstract. Then there is the middle area, more a fantasy area; that is where the fun stuff happens, like the Adium icon. No-one in their right mind would make it or think about it; the sport is to do it nonetheless."