Most online advertising works on a pay per click basis, so you need to have visitors and therfore a site worth visiting... People arent going to visit a site with nothing but adverts on. And many of the terms and conditions of online advertising prohibit adfarming. (This may be incorrect, it's been years since i looked into it.) The ones i can think of that made/ make millions were the "$1 per pixel, 1,000,000 pixels for sale" sites that mainly relied on a gimmick that could only work once, and places like youtube and myspace who get millions of hits every day. If making money online was really easy then everyone would be doing it...