The quote to the right pretty well sums it up but consider this: the most successful companies in the world and up and coming start-ups often pay 7 figures or more for the right domain name. These are some of the best and brightest marketers in the world. They wouldn't part with that much cash unless they were pretty sure of a substantial return on the investment.
For example, look at these past domain name sales . . .
Yes, your domain name is that important to the success of your enterprise. This is not a place to cut corners. Either you or one of your competitors is likely to own this domain name, and once it is sold it is unlikely to be available again - ever!
Today, your website is the lifeline of your business. It is more important than any single other asset you and your business can own. It's really where people find the information, and make decisions, about you and your product.
-- Rick Schwartz, Domain Name Investor