There is a nice thread going on at Cre8asite Forums named Is a Domain Name Worth It?, which discusses a blog entry by Barry Welford named Domain Names: the ultimate "vanity plates". You know something, I think it is worth quoting Bill Slawski's post once again, because he put so much detail into it.
There is a lot of value to a domain name.
1. Branding - By using your own domain name, you are working towards building an image that applies to your business. It is just one of many indicia that people see of the whole package, from business name, domain name, logo, tagline, mission statement, corporate history, to the more involved aspects of the business relationship with customers, vendors, competitors, and others who might interact with the organization.
2. Portability - you can take a domain name with you if you need to move from one server to another, or one host to another. IP addresses change, as do server names, if you find yourself on a service that provides a directory or a subdomain for your site instead of a domain name.
3. Memorability - a good domain name is easy to remember, and may lead to people not having to look the name up, or search for it amongst bookmarks or favorites.
4. Credibility - a domain name is more credible than just an IP address, or a directory or subdomain that includes the name of an ISP or shared host.
5. Type-in traffic - some domain names have value in that people will just type the address in a browser without knowing what might be on the other side, such as sex.com, or business.com.
6. Matching Offline Branding - branding efforts offline can be reflected on the web by the use of a well known business name or product name, or some other distinction about a business. This is true enough that a well known company will fight others under a trademark theory to take over a domain name that is in commercial use, or that is held by someone only with the intent of selling it to the trademark owner.
7. The appropriate tld - Chances are that if you are a commercial business that operates in a global environment, a name that uses the .com ending may be the most attractive choice for your business. Or, if you are a nonprofit, you would prefer one that ends with a .org. If you want to focus upon business in a country where local business is important, and search engines don't question your place of origin and business, a country specific two-letter tld may be of more value. The tld used in the domain name can be part of the value of a domain name by indicating what type of organization the site is, or where it is located.
At the WebmasterWorld conference there was a small discussion on domain names. In that discussion, Brett Tabke, the founder of WebmasterWorld, said that his logo is his domain name. What he meant by that is that he did not invest a whole lot on his logo because, as he said, "his best branding is the letters you type into the URL box in your browser when going to WebmasterWorld". It is a classic statement which shows the importance of a URL. I disagree with Brett in that I feel he should invest in a new logo that adds more to the WebmasterWorld brand, but I agree with his and Bill's views on a domain name.