Rand Fishkin over at SEOMoz has a great article titled "How to Avoid Needing an SEO" that talks about...well...how to know when you don't need to hire a search engine marketing consultant to be successful online.

It's a pretty honest and comprehensive look at the few things you can do that will make your site popular enough that you can do just fine without search marketing. A few examples? Offering up something amazing, or being the first and only player in your field.

It's a realistic post and it's true that there are a few companies (eBay, Coke, Nike) that can get away without using any type of search marketing or search advertising, but it also demonstrates the reality that it's a very rare company that CAN go without search marketing and still be as successful as they'd otherwise be.