I made over $23K in 30 days
(see proof) with my online business. That's been my biggest month so far, but I do make 5 figures a month. It's very simple to do when you know how to advertise your product/service. That's the key. Traffic. If you don't have a product or service... find someone who has one and market the heck out of it (direct sales).
In a lot of cases, you don't even need to "sell" the product yourself, just bring traffic to the website, let the website do the selling and cash in. That's what I do and I was able to retire from my full-time job back in January, 20th, 2006 with a 5-figure monthly income. Pretty sweet.
Leo