The link below has an interesting article about the kind of businesses you might wish to avoid running:

http://blogs.bnet.com/intercom/?p=2940

My thoughts on traffic-driven web-sites:

Traffic-driven web-sites , would have to be something really big like say Facebook or Google for you to make a living off the advertising revenue. The simple fact is that it is click-thru ads i.e. when the visitor to the site clicks through to actually visit the advertising business’ web-site. Also, if someone is at your web-site , however sticky , it may be, only a minute percentage of people actually click on the ads displayed. Say, if you have 100 visitors, if you’re lucky , then 5 may click through to the ads displayed. Thus, you need volumes to make your traffic-driven site pay for itself. Else, good luck !