It is always a good idea to secure potential misspellings of your domain name. I recently did a radio interview and at the end of the interview I provided my domain name. Unfortunately I did not take the time to actually spell it out. Upon realizing my error, I immediately went out and purchased multiple spellings of my URL to redirect to my main site.
This allowed me to capture all traffic from any listeners that may have had a different spelling of my site in mind, which increased my visitor rate from those who listened to the broadcast substantially.
Along with misspellings you should also consider purchasing plural and/or singular versions of your domain. I was doing research on some of my competitors and over the course of several weeks kept revisiting certain sites. One site in particular I had continuous trouble finding because I kept typing the domain name incorrectly. If I was the owner of grantasticdesigns.com I would also purchase and redirect the following:
Find all posts on Securing a Marketing-Rich Domain Name, or follow the links to previous posts.
Laying the Foundation for a Successful Online Business
Securing a Marketing Rich Domain Name Introduction
Build Your Brand
Secure a .com
Spell Words Properly
Multiple Domains: Type In Traffic