The widely reported recent case of a Tumblr user summarily losing control of a sub-domain and related blog has fanned the flames of discontent amongst users of hosted applications worldwide. The rumblings emerged again last year with Facebook's back down in the face of a user revolt. The more recent Tumblr case also reinvigorates the debate over the subtle difference between a name squat and genuine usage. In any event this incident reminds us exactly how frail the laws of ownership seem to be across the nebulous world of the Internet.
Whether it be Facebook, Twitter, Ning or any other service provider, they all have a point in common. You cannot own a web address such as http://facebook.com/yourusername or http://yourusername.tumblr.com because it is tied to THEIR domain name. If the domain (or company) fails for some reason you are not in control of your user-name and your content. Folks invest a lot of time building their online content and a deletion can be horrifying. So how does one go about protecting digital identity?
The domain name system (DNS) was invented in 1983 and .COM celebrates its 25th birthday this year. By 2012 there will be over 200 million domain names in use. Despite its age the DNS continues to provide reliable service to domain owners who enjoy complete control over how they use and manage their own domains. Unlike usernames, a domain is a secure asset whose operation is governed by a universal set of rules that registrars must operate within. The rules not only protect ownership, but also allow for full portability. You can transfer to a better registrar at any time and you can redirect your domain to any online service that you like.
You don't control your username...

...but you can control your own domain name

Source: http://www.identitywoman.net/personal-anchors-on-the-web-for-digital-identities
With the full implementation of internationalized domain names (IDNs) and the introduction of new top-level domains the diversity of available domain branding options will continue to grow. Many companies keep a small portfolio of branded domains for future use and to protect their digital identity from being misused. Under the domain industry rules a user may secure their personal domain without any obligation to apply it immediately. If an ownership dispute arises, there are rules governing this as well.
If you think your preferred user name might be controversial, at risk or already taken, why not choose a more generic name and then register a domain to control your digital identity instead?