From a brand perspective you want to ensure that your desired web properties are registered to you. This goes to say that if you have a website (that you care about) you should own the .COM, .NET, and .ORG domains, if available.
The small investment made to register these is worth the type of image you want to present to those who may either mistype or get re-directed from a search engine.
In the legal world, simply protecting your intellectual property, or trademarks, registering any domain names you can with your brand name in it is called defensive registration.
Whether you are a small business owner, or an executive at a large firm, it makes obvious sense that an investment as small as $10 and typically at the most $100 a year for a domain name makes sense. You want potential or current customers to land on your web property if they type in a domain name with your brand name in it.
(Photo credit: annaOMline)