Do you own your corporate domain name? It sounds kind of silly in 2008 doesn't it?
Let's go a level deeper. Do you own your personal .com name (i.e. www.mattdickman.com)?
That may be a bit more of a stretch for some of you, but it's crucial from a personal branding perspective. Just ask Shel Israel who did not have www.shelisrael.com purchased and someone else put up a site devoted to poking fun at him.
Other heavyweights like Robert Scoble (www.robertscoble.com) don't own their domain names either. Re-acquiring a domain name from a cybersquatter has some legal precedent, but it can rack of legal fees or large one-time purchase amounts.
Do you own your Twitter, YouTube and Flickr usernames?
However, let me ask you this. Do you own your personal/corporate Twitter username? How about your YouTube username? How about your Flickr username? If you don't, it's probably a good idea that you do (they're mostly free anyway). I lost out personally on my YouTube name because I used my nickname instead. You may not acquire them all, but you can sure try. These usernames do come up with search result pages adding to the importance of owning your identity.
The risk to your reputation that you run when somebody does register your username is potentially huge. There is no legislation (which I am aware of) that addresses these micro level identity-squatters. It could get to a point where people/companies have to pay for their usernames ala the late 1990's domain name deals.
Once you have acquired the usernames you will need to decide how, if at all, you use the account. While I don't like the fact that accounts may sit empty in the short-term, it is advisable that you secure your ID as soon as possible.
What are you waiting for? Go get your identity!
[Update: It looks like Shel Holtz and I are on the same page today. Check out his post on the same topic with FriendFeed.]