Targeting is very much possible, just as with magazines. If you have a recipes site you could have ads for kitchen tools. If you have a music site you have ads for local events. If you have lifestyle magazine you have clothing and interior ads. I would even go as far and say that this type of targeting is better then now when you go to a webshop, search for a product and suddenly starts seeing that product plastered all over the web, often even after you actually already bought the freaking product.