What kind of site do you have? Is it informational or are you selling or promoting something?

We recommend to all our web design clients to NEVER have ads on your site if you are promoting your business or e-commerce. Why would you want people leaving your site?? The amount that you could get for a pay per click would take a very long time to add up to a lost sale by someone clicking off your site. Take a look at all the major internet retail and promotional sites (IBM, CISCO, Target, Best Buy)out there...NONE have ads on them. All the major retailers could make a killing on pay per clicks since they get thousands of hits a day, but they do not do this. Why? Becuase they want people on THEIR site, buying THEIR products, making THEM money...not directing them to other sites!!!

I would think twice about adding advertisements to your site if the purpose of your site is to make you money!

Plus, having ads makes your site look broken up and cheap.

If you are an informational site, like a blog, where advertising would be the only possible source of income, then go for it.