here is
an article with pictures and stuff. this link is to page 2 of 2, the pics relavant to this discussion are about 3/4 down the page.
pasted directly from that:
Here is Brokguitar's list of the types of the bonuses you get for settling on top of a specific resource. You do not need the required technology to gain the extra FPC bonus provided by these resources.
Commerce Resources: When Dye, Gold, Gems, Incense, Fur, Silk, Silver, Spice, and Wine are next to a river, you will receive Two Extra Commerce when you settle on top of them.
Food Resources: When Bananas, Rice, Sugar, Sheep, Corn, Cows, and Pigs are on Grassland Tiles Only (no hills) you are able to produce One Extra Food when you settle on top of them.
Production Resources: When Coal, Copper, Iron, Marble, Oil, Stone, Aluminum, Horses, and Ivory are on Plains Tiles Only (not hills) you are able to produce One Extra Hammer when you settle on top of them.
Now if these same resources are on a Plains/Hill tile you can produce Two Extra Hammers.
--end of quote.
i settle on stone/marble/ plains ivory when the city cross makes sense. i lose a bit compared to turns i'd have somebody working the tile, but instead i get the bonus hammer every turn without ever having to find extra food to feed somebody working it. if the only way a city will work out is to settle on gems/silver/gold i collapse in a fit of tears.
edit for ezwip: if i'm understanding your question, "In other words if I build a city on a resource is there a chance of me getting less of a bonus due to that?", yes you do lose compared to turns you'd actually be working the tile. sometimes it's worth it IMO, and i don't think it makes you a moron, but i'm a permanoob so what do i know? see the article i linked above for waaaaaay more info.