I'm not here to preach, I'm just here to show evidence that Google is NOT the only source of good converting traffic, and that not only is it dangerous to focus your entire business just on SEO and Google, but if you ignore all other potential traffic sources - you are missing out BIG TIME.
Have a look at this graphic. This is taken from my Google Analytics account. This is for one of my own sites (data is captured for this entire year Jan til now) and as you can see, Google comes in 15th.
Sure Google has the potential to bring in a lot of traffic, but as many of you know, if you build your business JUST on Google (as Alexa always says) you're just one algorithm change away from total disaster.
(the section in shaded grey are conversions)